Answer
$\$1019.82 $ billion.
$\$232.82$
Work Step by Step
According to the Compound Interest Formula, where $P$ is the principal, the amount deposited, $r$ is the annual interest rate, $n$ is the number of times the interest is compounded annually, $t$ is the number of years, $A$ is the amount you get back after $t$ years:
$A=P\cdot(1+\frac{r}{n})^{n\cdot t}.$
Here we have: $t=20\text{ years}$
$r=1.3\%=0.013$
$P=\$787$
$n=2$ (since it is compounded semiannually)
Substitute these values into the formula above to obtain: $A=\$787\cdot(1+\frac{0.013}{2})^{2\cdot 20}\approx\$1019.82 .$ billion.
Then the interest is $\$1019.82-\$787=\$232.82$
