Question 1040250
a+c = 90 subtract c from both sides:
a = 90-c
:
2.25a+1.50c = 163.50 substitute for a:
2.25(90-c)+1.50c = 163.50
202.5-2.25c+1.50c = 163.50
-0.75c = -39
c = 52 were children, and 90-52 = 38 were adults
-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o
:
0.08x+0.11(22,000-x) = 1,835
0.08x+2,420-0.11x = 1,835
-0.03x = -585
x = 19,500 is invested at 8% and 22,000-19,500 = 2,500 is invested at 11% 
-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o
:
0.04(2x)+0.10x = 7,164
0.08x+0.10x = 7,164
0.18x = 7,164
x = 39,800 is invested at 4% and this is 2 times as much as she has invested at 10%: 39,800/2 = 19,900 is invested at 10%