At 1: 00 the water level in a pool is 13 inches at 2: 30 in the water level is 28 inches what is the rate of change

Let x = time, hours, from 1:00
Let y = water level, inches

Note that from 1:00 to 2:30, x = 2.5 - 1.0 = 1.5 hours.

The given data is
x:   0      1.5
y:  13   28.0

The change in x is 1.5 - 0 = 1.5 hours
he change in y is 28 - 13 = 15 inches

The rate of change is (15 inches)/(1.5 hours) = 10 inches/hour

10 inches per hour