x = transactions over 100, y = transactions under 100
x + y = 24.....x = 24 - y
3x + y = 32
3(24 - y) + y = 32
72 - 3y + y = 32
-3y + y = 32 - 72
-2y = -40
y = -40/-2
y = 20 <=== there were 20 transactions under $ 100
x + y = 24
x + 20 = 24
x = 24 - 20
x = 4 <==== there were 4 transactions over $ 100