What’s the answer and how do i solve this geometry question ? “find the missing side length”

The construction of copying qpr is started below. the next step is to set the width of the compass to the length of ab. how does this step ensure that a new angle will be congruent to the original angle? by using compass take the measures of angle and draw the same arc according to it.

The tiles on the left contain functions written using function notation . match each function with its input

Quickly select all numbers that are prime. 21 / 23 / 11 / 17 / 15