For home economics class, sandra has 5 cups of flour. she made 3 batches of cookies that each used 1.5 cups of flour. write and solve an expression to find the amount of flour sandra has left after making the batches of cookies

Because one batch of cookies uses up 1.5 cups of flour, we can write this as:

batch of cookies = 1.5 cups of flour 

Because she made 3 batches we can say:

batch of cookies  = 1.5 cup of flour * 3 (because she has made three)

This equals to 3 batches of cookies using up 4.5 cups of flour.

Because at the beginning she had 5 cups and she has used 4.5 cups of flour for making the batches of cookies, she is left with 0.5 cups of flour:

 5 cups at the start - 4.5 cups used for cooking = 0.5 cups in the end.