You have to find the change in the y-coordinate and divide it by the change in the x-coordinate.
So it would be (1 - (-4)) = 5 for the change in Y. And it would be (-10 - 0) = -10 for the change in X. So the final slope would be 5 divided by -10, which would result in -0.5.
There are 12 inches in one foot. If it rains 2 inches per hour and we need one foot we need to look for a number that can be multiplied by 2 to get 12. \
