The solution is indeed accurate.
Just add them
QM+MR=QR
16+x+2(x+2)=QR
16+x+2x+4=QR
20+3x=QR
Take any of the valid pairs of points, use the formula
rate of change = (y2-y1)/(x2-x1)
Say we use P1=(0,21.4), P2=(3,19)
x1=0, y1=21.4
x2=3, y2=19
Rate of change = (21.4-19)/(0-3)=2.4/(-3) = -0.8 sq. ft/in of liquid
Increases but is that what you are asking?
