If we consider that x is Edward's age, twice of his age is 2x and 3 more than that, 2x+3, is equal to his mom's age. so we can form an algebraic equation as follows.
2x+3 = 57
We should take +3 to the other side of the equation
2x+3 -3 =57-3
2x = 54
Isolate x: take 2 to the other side of the equation