Answer:
Matt used diameter of the ball instead of Radius
Step-by-step explanation:
The volume of a sphere is given as:
⇒ Matt made an error in his calculation by failing to covert the value of the diameter given to Radius.
⇒ By dividing the diameter by 2 = 15 / 2 = 7.5, we obtain the Radius, which is what Billy did in her own calculation.