A because I have done this before
The constant rate = 20 ft / 5 seconds = 4 feet per second
Find the chart that shows an increase of 4 feet for every second the balloon travels.
so, uh, i think the answe is actually 5. Since 5^2 is 25, minus 5 is 20, and 5 minus 1 is 4, 20 divided by 4 is 5. i hope that helps.
