In a keystone arch made with $15$ congruent isosceles trapezoids, let $x$ be the angle measure in degrees of the larger interior angle of a trapezoid. What is $x$?

1. Using the formula $x=90^\circ+\dfrac{90^\circ}n$ derived above, with $n=15$:
2. $x=90^\circ+6^\circ=96^\circ$.