Baylee wants to make 5 cups of a juice blend that contains 70% apple juice and 30% grape juice. She can get bottles of pure apple juice and bottles of a blend that are 50% apple juice and 50% grape juice. Let p represent the number of cups of pure apple juice and b represent the number of cups of the 50% apple juice/50% grape juice blend. What equation models the total volume of juice? Enter your answer in the box.