Question

-12
(42 + x)
= 21

Explanation:

Step1: Eliminate the coefficient

Multiply both sides by 2:
$$2 \times \frac{1}{2}(x+24) = 21 \times 2$$
$$x + 24 = 42$$

Step2: Isolate the variable x

Subtract 24 from both sides:
$$x + 24 - 24 = 42 - 24$$
$$x = 18$$

Answer:

$x=18$