Through: (4,4), slope
9/4

y - 4 = (9/4)(x - 4)

Step-by-step explanation:

Here we're given the slope (9/4) of a line and one point (4, 4) on the line.  The easiest form of the equation of a straight line to use here is the point-slope form:

y - k = m(x - h).

Here h = 4 and k = 4; the slope is m = 9/4.

Thus, the desired equation is

y - 4 = (9/4)(x - 4)

5   1/4   miles per hour

step-by-step explanation:

15   3/4 / 3 = 5   1/4