Answer:
a: C = $4.70d, (d ≤ 5, C = $4.70d - $1 ?: d ≥ 5, C = $4.70d)
b.(1) dvd returned after 4 days = ($4.70 × 4) - $1 ⇒ $18.8 -$1 ⇒ $17.8
(2) dvd returned after 7 days = $4.70 × 7 ⇒ $32.9
