Let us start with group I. Since it is given that there were 3 members, thus 3 food items were ordered totaling the bill of Rs 600. Thus we know pizza, a burger, and a dosa was ordered. SInce chef A can make pizza he will be making Pizza from 09:15 to 09:35(20 minutes). Burger and Pizza both take 15 minutes each. Chef B will start making any one of these from 09:15 to 09:30. And after this, e'll make the last food of the order from 09:30 to 09:45. Thus the food will be served at 09:45. Group will finish eating by 10:10. After sanitising the table will be again available at 10:20. The following can be represented as :
Thus group 2 coming at 09:30 ordered 2 sodas, 1 noodle, and a pizza. Since table 1 is occupied they will sit on table 2. Chef A will start working on their order at 09:35 whereas chef B will start working on the order from 09:45. To ensure the ordered is delivered in least time A will make 2 sodas and pizza.The remaining food item(noodle) will be made by B from 09:45 to 10:05. Thus the order will be served at 10:05. Group will finish eating by 10:30. Table 2 will be available by 10:40. It can be represented as
Group 3 will come at 10:00 and occupy table 3. The chef will start working on their order at 10:05. A will make Pizza and B will make a burger. Both orders will be served at 10:25. They will finish eating in 25 minutes. After which 10 minutes is taken for sanitization. The table will be available at 11:00
Group 4 comes at 10:10. They order 1 burger,1 dosa, and 1 soda. To minimize time soda will be made by chef B. Burger and Dosa both take 15 minutes each and can be made by either of them. One will make dosa and the r will make a burger. Order will be finished and served at 10:40.
Now group 5 came at 10:25. This time table 1 was available and hence will be occupied by them. Both chefs will get free at 10:40 and start cooking for group 5. One chef has to cook noodles which will take 20 minutes and another one will cook dosa which takes 15 minutes. Let us assume that A cooks noodle and B cooks Dosa( this assumption will not affect the solution as only 1 group is left to serve after group 5 and no further orders of Pizza are made)
Group 6 came at 10:30. But table 2 got free at 10:40 at the earliest. Hence they entered the restaurant at 10:40. There we 2 people hence 2 items were ordered worth 200. A possible combination is (burger and soda) or (Dosa and soda) or ( Sandwich and Noodles).
The 2 combinations (burger and soda) or (Dosa and soda) has a cooking time of 15 minutes+5minutes. In this case B will cook for 15 minutes and A will cook for 5 minutes to ensure that the order is made available at the least possible time. In this case, it will be possible at 11:10 am.
Combination of sandwich and noodle has a cooking time of 10 minute+20 minutes. B has to cook for 20 minutes and finish by 11:15 whereas A will cook for 10 minutes and finish by 11:10. Thus food will be served at 11:15
In question it was given that the food was served to them at 11:15 hence they ordered a sandwich and a noodle.
We can see that after 10:30 when group 6 occupied table 2, the next table to get free was table 3 at 11:00.