2018年1月1日，杨太太将 $15000 存入一个年复利率为 $R$% 的账户中。截至2021年1月1日，她共获得利息 $988.45。求 $R$ 的值。

1. Find the final amount after 3 years and set up the compound interest equation.

From 1st January 2018 to 1st January 2021 is $3$ years.

Total amount after 3 years
$=15000+988.45=15988.45$

Using compound interest,
$15000\left(1+\frac{R}{100}\right)^3=15988.45$

2. Solve for the annual interest rate.

$\left(1+\frac{R}{100}\right)^3=\frac{15988.45}{15000}$

$1+\frac{R}{100}=\sqrt[3]{\frac{15988.45}{15000}}$

$\frac{R}{100}=\sqrt[3]{\frac{15988.45}{15000}}-1$

$R=100\left(\sqrt[3]{\frac{15988.45}{15000}}-1\right)$

$R=2.15$