#### Answer

a) $\{9,8.1,7.29,6.561\}$
b) $h_n = 0.9^n(10)$

#### Work Step by Step

a) $h_n = rh_{n-1}$
$h_1 = 0.9h_0 = 9$
$h_2 = 0.9h_1 = 8.1$
$h_3 = 0.9h_2 = 7.29$
$h_4 = 0.9h_3 = 6.561$
b) We have to multiply the initial value $h_0$ by $r$, $n$ number of times.
$h_n = r^nh_{0} = 0.9^n(10)$