Question 418789
Let x = #cups of flour to make 3 dozen cookies

Using the ratios: (Cups of flour)/(number of dozens of cookies)

So we have 3.5/5 and x/3 meaning that

3.5/5 = x/3   
(3) * (3.5/5) = x
10.5/5 = x
2.1 = x

So the number of cups of flour to make 3 dozen cookies is 2.1 cups.