Use an addition or subtraction formula to find the exact value of the expression, as demonstrated in example 1.
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Can someone me out here number 4 plz

Solve the triangle. a = 21°, c = 105°, c = 5

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?