A gallon of milk makes $3 worth of butter because 2 x 1.5 = <<2*1.5=3>>3
A gallon of milk sells for the same amount as milk or butter because 3 = <<3=3>>3
She gets 48 gallons of milk because 4 x 12 = <<4*12=48>>48
She earns $144 selling the milk because 48 x $3 = <<48*3=144>>144
#### 144