PLZz help its due in 10 mins i will give brainliest

What is the value of x when x + 7 = 21?

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?

Find the value of x in the diagram below. select the best answer from the choices provided