Rosa bought a bag of apples. after she baked pies, she had 2/3 of a bag left. then she gave her cousin 3/4 of these, which was 9 apples how many apples did rosa have to start?

Great algebra problem!  We need to represent the unknown (which is the number of apples Rosa started with) with a letter, such as x.

After baking the pies, Rosa had (2x/3) apples left.

She gave her cousin (3/4) of (2x/3) apples.  This comes out to x/2 apples, which is 9 apples, according to the problem.  

Solve x/2 = 9 for x.  

Be certain to check your answer!

After baking the pies, she had 2/3 of a bag left, which is (2/3) of 18, or 12.

Is (3/4) of 12 equal to 9?

Draw your own conclusions.  Is x = 18 or not?  Justify your answer.

The answer to this question is c