A = Amount deposited by Mr. A
B = Amount deposited by Mr. B
B = A + 1200
Interest for Mr. A: IA = A * 0.07 * (18/12)
Interest for Mr. B: IB = B * 0.09 * (12/12)
IB - IA = $27,75
Can you finish?
For your benefit, let's see if I can re-translate for you.
Mr. A deposited a given amount with an annual interest rate of 7%. After 6 months, Mr B deposited $1200 more than Mr A, but with an anual interest rate of 9%. After 18 months from the first deposit (by Mr A), Mr B recieved interest of $27,75 more then Mr A.
Use Simple Interest and determinate how much was deposited by each.