A cup is 250 mL.
1 gallon in the US is 3.78 L * 1000 mL / 1 L = 3780 mL
1 gallon contains 3780 / 250 = 15.12 cups.
So the number of gallons for the punch = 4 + 1 + 1 = 6 gallons.
1 gallon gives 15.12 cups
6 gallons will give x
1/6 = 15,12/x
x = 6 * 15.12
x = 90.72 cups. That's for an awfully big party.