A puppy weighed 4 ounces (oz) at birth and gained 5 oz each week for the first 10 weeks. The equation that models the puppy's weight, y, after x weeks is
a. y = 4 + 5x
b. y = 4 × 5ˣ
c. y = 4 + x⁵
d. y = 4 ÷ 5ˣ