Explanation:

To solve this, we need to find a number 'x' that makes 7, 4, and 2 in continued proportion when each is increased by 'x'. Continued proportion means:

1. `(7 + x) / (4 + x) = (4 + x) / (2 + x)`

Checking each option:

- Option 1: Add 2

- (7+2)/(4+2) = (4+2)/(2+2)

- 9/6 ? 6/4

- This doesn't work.

- Option 2: Add 4

- (7+4)/(4+4) = (4+4)/(2+4)

- 11/8 ? 8/6

- This doesn't work.

- Option 3: Add 3

- (7+3)/(4+3) = (4+3)/(2+3)

- 10/7 = 7/5

- Both sides are equal when put in ratio.

- Option 4: Add 5

- (7+5)/(4+5) = (4+5)/(2+5)

- 12/9 ? 9/7

- This doesn't work.

Correct Answer: Option 3, Add 3