1) x + y = 16,000 or x = 16,000 - y
2) 0.05x + 0.06y = 810
substitute eq(1) into eq(2):
0.05(16,000 - y) + 0.06y = 810
800 - 0.05y + 0.06y = 810
0.01y = 10
y = 10/0.01 = $1,000
using eq(1):
x = 16,000 - 1000 = $15,000
He invested $15,000 at 5% and $1,000 at 6%
check using eq(2):
0.05(15,000) + 0.06(1,000) = 810
750 + 60 = 810