One ingredient of a recipe is 3/8 cup of milk. what part of a cup is needed to make one-half of the recipe?

To make the full recipe, you need 3/8 cup of milk. Multiply this value by 1/2 to figure out how much of this is needed for only half the recipe

(1/2)*(3/8) = (1*3)/(2*8) = 3/16

So you'll need 3/16 cup of milk to make one-half of the recipe