Consider the algebraic expression $W-(X-(Y-(Z+K)))$. A common student error is to simplify such expressions by ignoring parentheses and applying the leading sign to the first term of each parenthesized group, then treating the rest linearly. Thus, the student calculated the expression as $W-X-Y-Z+K$. If this calculation yielded the correct result by coincidence, and the values substituted for $W,X,Z,$ and $K$ were $100,50,20,$ and $15$ respectively, what was the value substituted for $Y$?