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The inverse version of a number is it's opposite. The opposite of 3 is -3
You multiply by 2 because if you take any number let's say 15, 15x 6 is 90 1/3 of 90 is 30 and 15 is half of thirty. this works with all numbers so the answer is dilate by a scale factor of 2.

In the given figure, NQ acts as a diameter and since diameter subtends 90° at the arc of the circle, so we can conclude that ~



Now, Let's use Angle sum property of Triangle to solve for z :







I hope you understood the procedure, you can ask me in comments if you have any doubts.