Layna can paint a 350-square-foot room in 4 hours. it takes bebe 7 hours to paint the same room. which equation can be used to find t, the time it takes layna and bebe to paint the room together?

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?