.
x = invested at 3%;
(x+1000) = invested at 5%;
the rest, (16000-x-(x+1000)) = 15000-2x invested at 6%.
The total 1-year interest
0.03x + 0.05(x+1000) + 0.06(15000-2x) = 900.
Simplify and find x
0.03x + 0.05x + 50 + 900 - 0.12x = 900
0.03x + 0.05x - 0.12x = 900 - 50 - 900
-0.04x = -50
x = = 1250 dollars.
ANSWER. $1250 invested at 3%; $2250 invested at 5%; and the rest, 16000-1250-2250 = 12500 invested at 6%.
CHECK. 0.03*1250 + 0.05*2250 + 0.06*12500 = 900 dollars, the total annual interest. ! Precisely correct !
Solved.