Question

1. $6 + 3x = 21$

Explanation:

Step1: Subtract 6 from both sides

$6 + 3x - 6 = 21 - 6$
Simplify to get: $3x = 15$

Step2: Divide both sides by 3

$\frac{3x}{3} = \frac{15}{3}$
Simplify to get: $x = 5$

Answer:

$x = 5$