1 batch need 3/4 gallon of milk
She has 1/4 gallon cup
(3/4) divided by (1/4)
A technique in math is just flip the divider which is (1/4) to (4/1)
so it becomes (3/4) multiply (4/1) = (3x4) / (4x1) = 12/4 = 3 times for one batch
She needs three batches so 3 x 3 = 9 times to fill the measuring cup to make all 3 batches of milkshake.