1 cup has = 12 oz of lemonade
so 50 cups have = 50 * 12 = 600 oz of lemonade.
now, 1 oz = 0.0078 gallons
600 oz = 0.0078*600 = 4.68 gallons.
Hence to fill 50 cups they need 4.68 gallons of lemonade.
part 2:
1 oz = 0.03125 quart
12 oz = 0.03125 * 12 = 0.375 quart
So 1 cup will hold 0.375 quart of lemonade.
and 50 cups will hold =0.375 * 50 = 18.75 quart of lemonade.
Now 1 quart = 0.25 gallons
so 18.75 quarts will have 0.25 * 18.75 = 4.68 gallons
Hence by comparing the values and comparing the statements of Jackson and Derek, both of them have said the same thing but in different units.
Both amounts are enough to fill 50 12 oz cups.