Answer:
[tex]\large \boxed{\$13 200}[/tex]
Step-by-step explanation:
The formula for simple interest I is
I = Prt, where
P = the principal (amount invested)
r = the interest rate per period and
n = the number of periods
In this problem, the interest rate is annual, so n = 1.
We must write the interest rate as a decimal fraction.
Let x = amount of each investment. Then
0.02x = interest at 2 %
0.07x = interest at 7 %
0.09x = interest at 9 %
0.18x = total interest
[tex]\begin{array}{rcl}0.18x & = & 792\\x & = & \dfrac{792}{0.18}\\& = & 4400\\\end{array}\\\text{Each investment was \$4400.}\\\text{The total investment was 3$\times \$4400$ or $\large \boxed{\mathbf{\$13 200}}$}[/tex]
