The question asks in other words: in a pie there is 1/4 cup of sugar. How much sugar in 1/5 of the pizza?

The answer should be 1/5 of 1/4. In fraction language it is written as:

1/5 x 1/4 = (1 x 1) /(5 x 4) = 1/20 of a cup of sugar in each pizza slice.