# What is the value of 4x + 9, when x = 4?

## Question:

What is the value of 4x + 9, when x = 4?

## Substituting the Value of a Variable:

When we are given the value of a variable and asked for the value of a formula that includes the variable, we start by replacing the variable with its value. If the formula includes a multiplying of the variable, such as 3y, and we are told that y = 6, we would write this in parentheses as {eq}(3 \times 6) {/eq}.

## Answer and Explanation: 1

4x + 9 equals 25, when x = 4.

Since we are given the value of our variable, we substitute its value for the variable as our first step.

• {eq}4(4) + 9 {/eq}
• {eq}16 + 9 {/eq}

Now, we simply add to get the answer.

• {eq}16 + 9 = 25 {/eq}

#### Learn more about this topic: What is a Variable in Algebra?

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Chapter 6 / Lesson 1
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Did you ever encounter something like a + b = c and wonder how all these letters snuck into a math problem? In this lesson, we'll learn about variables, as well as other parts of equations, constants and coefficients.