A cookie recipe for 60 cookies calls for 4 cups of flour. How much flour is needed to make 90 cookies.

✨6 cups of flour.✨

so the recipe says 60 cookies but you need 90.
so ask yourself how do you get from 60 to 90 (what number can you multiply with 60 to get to 90)?
you can set up an equation like this:
60x=90
x=90/60
x=3/2