Let x be the amount, in dollars, invested at 7%. Then the amount invested at 8% is 2x dollars, and the amount invested at 9% is 3x dollars. Then the equation expressing total interest of three accounts is 0.07x + 0.08(2x) + 0.09*(3x) = 200 dollars. Simplify 0.07x + 0.16x + 0.27x = 200 0.5x = 200 x == 400. ANSWER. $400 invested at 7%; $800 invested at 8% and $1200 invested at 9%. CHECK. 0.07*400 + 0.08*800 + 0.09*1200 = 200 dollars, which is PRECISELY correct (!)