Question

Given ƒ(x) = 9x + 54, find x when ƒ(x) = 18.
A)−6 B)−4 C)3 D)8

Answer 1

B. -4

Explanation:

We want to find x such that f(x)=18.

We need to therefore solve 9x+54=18 forx.

9x+54=18

Divide both sides by 9:

(9x+54)/9=18/9

9x/9+54/9=18/9

Simplify:

x+6=2

Subtract 6 on both sides:

x=2-6

Simplify

x=-4.

So f(-4) should have value 18.

Let's check.

f(x)=9x+54

f(-4)=9(-4)+54

f(-4)=-36+54

f(-4)=18

So the answer is B.

Answer 2

The value of x when
`f(x)=18` is -4

Explanation:

Expression :
`f(x)=9x+54`

We are given that
`f(x)=18`

We are supposed to find the value of x when
`f(x)=18`

So, Expression :
`f(x)=9x+54`

Substitute
`f(x)=18`

`18=9x+54`

`18-54=9x`

`-36=9x`

`(-36)/(9)=x`

`-4=x`

So, option B is true

Hence the value of x when
`f(x)=18` is -4