Question

If $x=-2$, then $15-3\left(x+1\right)=$?

$\left(A\right)6\left(B\right)12\left(C\right)18\left(D\right)21$

Short answer

The option $\left(C\right)$is correct, the other options are incorrect, because the value of the expression $15-3\left(x+1\right)$when $x=-2$ is 18.

Step-by-step solution

– Use the substitution method to find the value of the given expression.

Substitute $x=-2$in $15-3\left(x+1\right)$:

$\begin{array}{c}15-3(x+1)=15-3(-2+1)\text{substitute}-2\text{for}x\\ =15-3(-1)\text{\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}simplify}\\ =15+3\\ =18\end{array}$

So, $15-3\left(x+1\right)=18$when $x=-2$.

– Check whether the option Ais correct or incorrect.

Here, in the option $\left(A\right)$it is given that, 6.

The result in step 1 is $15-3\left(x+1\right)=18$.

So, option $\left(A\right)$is incorrect.

– Check whether the option Bis true or false.

Here, in the option $\left(B\right)$it is given that 12.

The result in step 1 is $15-3\left(x+1\right)=18$.

So, option $\left(B\right)$is incorrect.

– Check whether the option Cis true or false.

Here, in the option $\left(C\right)$it is given that 18.

The result in step 1 is $15-3\left(x+1\right)=18$.

So, option $\left(C\right)$is correct.

– Check whether the option Dis true or false.

Here, in the option $\left(D\right)$it is given that 21.

The result in step 1 is $15-3\left(x+1\right)=18$.

So, option $\left(D\right)$is incorrect.

Hence, the option $\left(C\right)$ is correct, the other options are incorrect, because the value of the expression $15-3\left(x+1\right)$when $x=-2$ is $18$.