we know that
1 1/4 cups of sugar to make 20 cookies
so
Applying proportion
Find out how many cups of sugar to make 6 cookies
but first
convert mixed numbers to an improper fraction
1 1/4=1+1/4=5/4 cup of sugar
(5/4)/20=x/6
solve for x
x=[(5/4)/20]*6
x=(5/80)*6
x=30/80
x=3/8
the answer is 3/8 cups of sugar