Solution:

Given, the four bells toll together at 9:00 A.M. after 7, 8, 11 and 12 seconds respectively.

We need to find out how many times they will toll together again in the next 3 hours.

Let's first calculate the time taken by each bell to toll again after the first toll at 9:00 A.M.

- The first bell tolls again after 7 seconds.
- The second bell tolls again after 8 seconds.
- The third bell tolls again after 11 seconds.
- The fourth bell tolls again after 12 seconds.

We need to find out the LCM (Least Common Multiple) of 7, 8, 11 and 12 to determine the time taken by all four bells to toll together again.

Calculating LCM:

- 7 = 7 × 1
- 8 = 2 × 2 × 2
- 11 = 11 × 1
- 12 = 2 × 2 × 3

LCM of 7, 8, 11 and 12 = 2^3 × 3 × 7 × 11 = 1848 seconds.

This means all four bells will toll together again after 1848 seconds or 30 minutes and 48 seconds.

Now, we need to find out how many times all four bells will toll together in the next 3 hours, i.e., 180 minutes.

Calculating number of times:

- Number of times in 1 hour = 60 minutes/30.8 minutes (time taken by all four bells to toll together) = 1.95
- Number of times in 3 hours = 3 × 1.95 = 5.85
- As we cannot have fractional tolls, we need to take the floor value of the number of times, which is 5.

Therefore, all four bells will toll together 5 times in the next 3 hours.

Answer: All four bells will toll together 5 times in the next 3 hours.

Then next time all the bell will ring together can be found by finding the LCM of the given seconds... Which will be 1848.... So the bell will ring 1st time after 1848 seconds... Another will ring in next 1848 seconds and so on.... i.e. The bells will ring together at every 1848 seconds...
Now we have given 3 hours.. Which Is 10800 seconds ( 1hr=3600 sec). So 10800/1848 =5.84...
So all together will ring for 5 times in next three hours..