Twenty-five is nine more than four times a number

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The phrase a number means an arbitrary variable. We can pick any letter a-z except for i and e.

Let's choose x.

Four times a number:
4x

nine more than four times a numbrer
4x + 9

The phrase is means equal to. We set 4x + 9 equal to 25 as our algebraic expression:
4x + 9 = 25

If the problem asks you to solve for x, we type it in our math solver and get:
x = 4