Easy! If Smith had four daughters who each had 4 kids, then he had a total of 20 kids. I got this by multiplying the daughters by their kids, 4x4, and adding the four daughters, so it equals 20 kids in total!
Hope it helps!
The rate of change is the slope of this line
m = (y2 - y1)/(x2 - x1) = (13 - 5)/(4 - 0) = 8/4 = 2
Pi r² is circle's area expression.
So the r is radius,.
