Question

How do you figure out 16???

Answer 1

since BA ≅ BC, that means is an isosceles triangle, whose twin sides make twin angles at the base, namely the interior angles at A and C are both twin angles, and their exterior angles at those point are also twins, check the picture below.

that simply means that "x" and "y" are linear angles, therefore

x + y = 180°

117 + y = 180

y = 180 - 117

y = 63.