Answer:
total balloons = 120r+72y
Step-by-step explanation:
If there are 120 cases of red balloons and r red balloons in each cases
Number of red balloons = 120*r
If there are 72 cases of yellow balloons and y yellow balloons in each cases
Number of yellow balloons = 72y
The total number of balloons is red balloons plus yellow balloons
total balloons = 120r+72y