Answer:
Brandy will save $315 in 21 weeks.
Step-by-step explanation:
Let x be the number of weeks.
If in a week, he saves $15, then in x weeks he will save 15x.
15x = 315
To find the number of weeks, divide 315 by the money saved in a week.
x = 315 ÷ 15
x = 21
21 weeks.