What does the question mark represent if the area of this shape is 21

Successful implementation of a new system is based on three independent modules. module 1 works properly with probability 0.96. for modules 2 and 3, these probabilities equal 0.95 and 0.90. compute the probability that at least one of these three modules fails to work properly.

Points a, b, and c form a triangle. complete the statements to prove that the sum of the interior angles of triangle abc is 180

Sate why the measure of angle d is 120 degrees