Question 1091229
Let n = the number bought
Let p = the price of each shirt
Then p*n = 720 -> p = 720/n
Also (p-2)(n+4) = 720 -> (720/n-2)(n+4) = 720
720 + 720*4/n - 2n - 8 = 720
n^2 + 4n - 1440 = 0
This factors as:
(n+40)(n-36) = 0
Take the positive solution, n = 36
The number of shirts bought is 36.