problem: Let $\Psi$ be the relation defined by $A\ \Psi\ B=2A+5B$. What is the value of $9\ \Psi\ (3\ \Psi\ 1)$?
solution: Substitute 3 for $A$ and 1 for $B$ in the expression defining $\Psi$ to find $3\ \Psi\ 1=11$.  Then substitute 9 for $A$ and 11 for $B$ to find $9\ \Psi\ 11=2\cdot 9+5\cdot 11=\boxed{73}$.