Answer:
24 cups, 48 plates, 12 balloons
Explanation:
In order to solve for the amount of each item, you can assign one variable and two expressions all of which will have a sum of 84.
c = the number of cups
2c = the number of plates (twice as many plates as cups)
0.5c = the number of balloons (half of the number of cups)
There was a total of 84 items:
c + 2c + 0.5c = 84
Combine like terms: 3.5c = 84
Divide: 3.5c/3.5 = 84/3.5
Solve for c: c = 24 (cups)
2c = 48 (plates)
0.5c = 12 (balloons)