We would use the distributive property, then add 28, and, finally, divide by 21.
Work Step by Step
The distributive property allows us to distribute anything multiplied by something inside of the parenthesis to whatever is inside of the parenthesis. Thus, we distribute the 7 to everything inside the parenthesis, giving us $21x-28=49.$ We now need to get the x alone. Thus, we cancel out the subtraction by adding 28 on both sides. Finally, we use division, so we divide both sides by 21 to isolate x.