please help I thought Ik what I was doing... I really don't so help me just give me a step my step something that can help ​

What is the range? can’t seem to find it out

Precalculus question, image attached.

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?