# If f(7) = 18, then how do you complete f(x) = 2x + _____?

Jul 5, 2015

$f \left(x\right) = 2 x + 4$

#### Explanation:

$f \left(7\right) = 18$$\text{ } \textcolor{red}{\left(1\right)}$

Let

$f \left(x\right) = 2 x + B$

Where B is the value to be determined.

Replace $x$ by 7 in above equation.

$f \left(7\right) = 2 \left(7\right) + B$

$f \left(7\right) = 14 + B$

But we know that $f \left(7\right) = 18$,

$18 = 14 + B$

$B = 18 - 14$

$B = 4$