There are two towns, A and B. In A, population decreases by 10,000 every year. In B, population increases by 15,000 every year. What should be the difference between initial populations of B and A if their population becomes equal after 30 years?

Correct option is B

Let town A have initial population x and town B have initial population y.
After 30 years:

Town A:
x − 10,000 × 30

Town B:
y + 15,000 × 30

Their populations will be equal:

$$x - 10{,}000 \times 30 = y + 15{,}000 \times 30$$

Solving for the difference in initial populations:

$$x - y = 10{,}000 \times 30 + 15{,}000 \times 30$$​

$$x - y = (10{,}000 + 15{,}000) \times 30 = 25{,}000 \times 30 = 750{,}000$$​