Assuming that 1 batch contain 12 muffins, and 32 batched can be made with 1 gallon of milk, the calculation is :
# the batches the bakery make everyday
96 : 12 = 8 batches/ day
which means the bakery make 240 batches for 30 days
Since 1 gallon of milk is enough to make 32 batches, that bakery need 240 : 32 = 7.5 Gallons of milk every 30 days