You need to use the formula of compound interest such that:

`A = P(1 + i)^n`

A represents the final amount

P represents the invested amount

i represents the interest rate per period

n represents the number of compounding periods

The problem provides the value of P = $20, 000...

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You need to use the formula of compound interest such that:

`A = P(1 + i)^n`

A represents the final amount

P represents the invested amount

i represents the interest rate per period

n represents the number of compounding periods

The problem provides the value of P = $20, 000 and the fact that the 4% interest is compounded quaterly, meaning that you may evaluate n such that:

`n = 10*4 = 40` periods

`i = (4%)/4 => i = 0.04/4 => i = 0.01`

You may evaluate A such that:

`A = 20,000(1 + 0.01)^40 ~~ 29,777`

**Hence, if Susan invests $20,000 in a savings account that pays 4% interest compounded quarterly, the final amount, after ten years will be A = $29,777, which is very close to the sum she needs, but a bit under $ 30,000.**