Parentheses when Substituting

Do you sometimes think, "I wish my students could just remember this one thing?"

I'd like mine to remember to use parentheses when substituting into an algebraic expression.  I stress outlining the problem before replacing the variables with numbers.  However, I can't force students to do it.  It can be frustrating because if they do outline the problem first, as shown below, they generally solve it correctly.

One little trick I use when working examples for the class is to highlight each space where a number will be substituted.  Little things like this can help put the focus where it belongs, and is especially helpful to students who are visual learners.