You
are mowing lawns to make some extra money. The amount of money you make
varies directly with the number of lawns you mow. If you mow 5 lawns
and earn $50, what is the constant of variation?

Let x be the number of lawns you mow and y be the amount of money you earn for it. Then y = kx, where k is the variation constant. For x = 5 we get y = 50, that is, 50 = 5k and k = 10.

The answer is c).

19. The domain of the relation is the set of all values of the x-coordinates of the points A, B, C, D, and E. There are only three such values: 0, 1, and 2.