Income flows into the coffers of ACME BirdTraps $($ABT$)$ at the rate

f$($t$)=600$t $+1200$

$($a$)(2$ pts$)$ Find the nominal value of ABT's income flow over a period of $20$ years.

$($b$)(3$ pts$)$ Find the present value of ABT's income flow of a period of $20$ years, assuming that the interest rate is r $=4\mathrm{.}5\%$

$($c$)(1$ pts$)$ Find the present value of ABT's income flow, assuming that the interest rate is r $=4\mathrm{.}5\%$ and that the income flows indefinitely $($i$.$e$.,$ "forever"$).$