When two triangles are congruent, their corresponding sides and angles are equivalent. Since ∠W and ∠S are two corresponding angles, their measures will be equal to each other. We're given that m∠W = 8n + 10 and m∠S = 10n - 24, so we can set up an equality between the two:
8n + 10 = 10n - 24
Moving the 8n over to the right side by subtraction and the 24 over to the left side by addition, we get
10 + 24 = 10n - 8n
34 = 2n
and dividing both sides by 2 to get n by itself gives us
17 = n