We are asked to write an algebraic expression for the given verbal expression. The key phrase in the verbal expression is the difference of ... This indicates that we should subtract two things in specific order.
... - ...The two terms that we are subtracting together are a number y and 9. Since the expession says The difference of a numbery and 9 the ynumber should be on the left-hand side of the subtraction.
y - 9
We are also asked to evaluate this expression when y= 12. This means that we should substitute 12 for y in the given expression and then evaluate. Let's do it!
