Explain why these two equations have the same solution. Do not calculate the solution.
3 × m + 4 = 25 and 3 × m = 21
3m + 4 = 25 <--- the original equation
3m = 25-4
3m = 21 <----- the equation after subtracting 4 from both sides
This is a proper step to take, so the two equations are equivalent.