Answer:
18 weeks
Explanation:
Let the number of weeks be represented by a variable x;
Beginning balance = 450
Ending balance= 180
Amount spent per week= 15
Amount spent in x weeks = 450-180= $270
Total amount spent in x weeks = 15*x = 15x
Equate the above equations to the corresponding dollar amount;
15x=270
Next, solve for x by dividing both sides by 15
x=270/15
x= 18
Therefore, there are 18 weeks in the semester.