If there are 16 cups in one gallon, each gallon u add 16. If you have 3 gallons you add 16 3 times. So to get your answer you multiply 16 by three which is 48 cups.
You can Calculate the mass of magnesium sulphate obtained from 5g of magnesium.
X
=
u
y
−
k
y
is the answer
x= u/y - k/y