The recipe is
1/4 cup water for every 1/2 cup of flour.
let x represent the number of cups of flour needed for 1.5 cups of water. The equation would be
1/4 = 1/2
1.5 = x
Crossmultiplying, it becomes
1/4 * x = 1.5 * 1/2
0.25x = 0.75
x = 0.75/0.25
x = 3
3 cups of flour would be needed for 1.5 cups of water