**Problem Statement:**
A body travels 200 cm in the first 2 seconds and 220 cm in the next 5 seconds. We need to calculate the velocity at the end of the seventh second from the start.

**Solution:**
To solve this problem, we can use the concept of average velocity. Average velocity is defined as the total displacement divided by the total time taken.

**Step 1: Calculate the total displacement:**
We are given that the body travels 200 cm in the first 2 seconds and 220 cm in the next 5 seconds. Therefore, the total displacement can be calculated by adding these two values.
Total displacement = 200 cm + 220 cm = 420 cm

**Step 2: Calculate the total time taken:**
The total time taken is equal to the sum of the time taken in the first 2 seconds and the time taken in the next 5 seconds.
Total time taken = 2 s + 5 s = 7 s

**Step 3: Calculate the average velocity:**
Average velocity is given by the formula:
Average velocity = Total displacement / Total time taken

Substituting the values, we get:
Average velocity = 420 cm / 7 s = 60 cm/s

**Step 4: Calculate the velocity at the end of the seventh second:**
To find the velocity at the end of the seventh second, we need to calculate the change in displacement during the seventh second and divide it by the time taken in that second.

Change in displacement during the seventh second = Displacement in the first 2 seconds + Displacement in the next 5 seconds
= 200 cm + 220 cm = 420 cm

Time taken during the seventh second = 7 s - 6 s = 1 s

Velocity at the end of the seventh second = Change in displacement during the seventh second / Time taken during the seventh second
= 420 cm / 1 s = 420 cm/s

**Conclusion:**
Therefore, the velocity at the end of the seventh second from the start is 420 cm/s.

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