Answer:
25
Explanation:
3t+15=90
3t=75
t=25
t represents the price for one t-shirt. 90 is the total amount and if the booklet is 15 dollars, altogether they equal 90. With this equation you are trying to isolate the variable (t), so subtract 15 because the opposite of 15 is -15. Then divide that by 3 because 3t is also 3 times t and the opposite of times is division.