Rate of flour to sugar: 2[ggfrac]1/4[/ggfrac] / 1[ggfrac]1/2[/ggfrac]
Unit rate of flour to sugar:
2[ggfrac]1/4[/ggfrac] / 1[ggfrac]1/2[/ggfrac] = [ggfrac]9/4[/ggfrac] x [ggfrac]2/3[/ggfrac] = [ggfrac]18/22[/ggfrac] = [ggfrac]3/2[/ggfrac] cups of flour for every cup of sugar
Multiply [ggfrac]3/2[/ggfrac] × 9 to find out how much flour she needs:
[ggfrac]3/2[/ggfrac] x 9 = 13[ggfrac]1/2[/ggfrac] cups of flour
Sandra needs 13[ggfrac]1/2[/ggfrac] cups of flour to make the cookies with 9 cups of sugar.