Answer
a. 90
b. 270
c. 8000
Work Step by Step
a. $p=0.06(s-500)$ with $s=2000$
$p=0.06(2000-500)$
$p=0.06(1500)$
$p=90$
b. $p=0.06(s-500)$ with $s=5000$
$p=0.06(5000-500)$
$p=0.06(4500)$
$p=270$
c. $p=450$
$450=0.06(s-500)$
$450\div0.06=s-500$
$7500=s-500$
$7500+500=s$
$s=8000$