Use the rules for inscribed angles here: an inscribed angle is half the measure of the arc it intercepts. If angle N is 86, then its intercepted arc is 172. We already have part of its intercepted arc as 94, so arc RQ is 78. If angle S is 78, then it is half the measure of its intercepted arc and we already have part of it: 78. Therefore, the other arc, the one you're looking for, is 78.
