9 is the answer because 1/3 = 3
The rate of change is -6 because it’s being subtracted by 6 each time.
In any trapezoid, the area is given by

where B and b are the two bases, and h is the height. You're given all these elements already, so you only need to plug the values in:

<span>28 is 32% of 87.5.
</span><span>0.32x = 28
x = 28/0.32
x = 87.5
</span>