Distance Formula. I think I’m supposed to use that but like my teacher said it was wrong and like I’m so confused I need help!!! BTW #16 (goes with the graph)

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?