EXPLANATION
The compound interest formula is
[tex]A=P(1+\frac{r}{n})^{nt}[/tex]P= Principal = $10,000
Interest rate = 8.4% = 0.084 in decimal form
n= Number of times interest rate is compounded per unit "t" = 12
t= Time = 30 years
Replacing terms:
[tex]A=10,000(1+\frac{0.084}{12})^{12\cdot30}[/tex]Multiplying and dividing numbers:
[tex]A=10,000(1+0.007)^{360}[/tex]Adding numbers:
[tex]A=10,000\cdot\text{1}.007^{360}[/tex]Solving the power:
[tex]A=10,000\cdot12.32[/tex]Multiplying terms:
[tex]A=\text{ 123,200}[/tex]Sally will have $123,200 in 30 years.