Answer: He will be running 45 miles in the during the fifteenth week of school.
Explanation:
Given: Joshua runs each day after school to train for his cross country team.
He ran 3 miles in first week, 6 miles in second week, 9 miles in third weeki.e. sequence will be 3, 6, 9 ,....(multiple of 3.)
The number of miles he will be running during the fifteenth week of school = 15 x 3
=45
Hence, he will be running 45 miles in the during the fifteenth week of school.