At 1: 00 pm the water level in a pool was 13 inches at 1: 30 pm the water level is 18 inches at 2: 30 pm the water level is 28 inches. what is the constant rate of change

Look at the figure below: triangle abc is a right triangle with angle abc equal to 90 degrees. the length of ac is 5 units and the length of ab is 4 units. d is a point above c. triangle adc is a right triangle with angle dac equal to 90 degrees and dc parallel to ab. what is the length, in units, of segment cd?