A stationary Buy a gel pen for rupees 20 and sell it at 20% for what price should he buy it so that he can make 25% profit by selling for the same selling price

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?