I am assuming that the 34 3 4 cup of sugar means 34 3/4.
Given:
Ratio of sugar to water is 1:4
34 3/4 sugar to quantity of water.
First, we need to convert the mixed fraction into an improper fraction.
34 3/4 = ((34*4)+3)/4 = 139/4
1:4 = 139/4:x
x = 4*139/4
x = 139
Jenny should use 139 cups of water for the 34 3/4 cups of sugar.