# Evaluate the expression 3z + 3

by By a Visitor

**Question**

Evaluate the expression 3z+3 when z = 5.

I say the answer is 15, my son says the answer is 18. We have been arguing over this for 20 minutes. I told him it was a trick question that they were just looking for the expression not the solution.

**Answer**

I have to agree with your son. This is because 3z+3 is an expression. To briefly elaborate, an expression is like a mathematical 'phrase'. Hence, this expression is a 'phrase' described by 2 terms, which are

*3z* and

*3*.

So, when we evaluate 3x + 3, both terms must be included in the calculation. This is shown below:

Substitute z with

**5**:

**3(****5****) + 3 **

Now, we just need to perform some simple calculations and we will arrive at the answer 18.

**3(****5****) + 3 ** = **15 +3 = **__18__

This site has a animated math video on Evaluating Expression that may be of interest to both of you (scroll down the page to see the video).

The link is given below:

- Lesson on Evaluating Expression