Answer
a) $\{15,11.25,8.4375, 6.328125\}$
b) $0.75^n(20)$
Work Step by Step
a) $h_n = rh_{n-1}$
$h_1 = 0.75h_0 = 15$
$h_2 = 0.75h_1 = 11.25$
$h_3 = 0.75h_2 = 8.4375$
$h_4 = 0.75h_3 = 6.328125$
b) We have to multiply the initial value $h_0$ by $r$, $n$ number of times.
$h_n = r^nh_{0} = 0.75^n(20)$