x = hours tutoring
y = hours shoveling snow
so Kayla will be tutoring for "x" hours at 20 bucks a pop, so she'll make a total amount of 20*x or 20x.
Kayla is going to be shoveling snow "y" hours at 15 bucks a pop, so she'll make the whooping amount of 15*y or 15y.
whatever "x" and "y" are, their sum must be no more than 3
x + y ⩽ 3
whatever the sums of 20x and 15y are, their sum must be at least 50 bucks
20x + 15y ⩾ 50