All real numbers
Work Step by Step
In order to solve the equation, we must first get the terms with variables all on one side of the equation and the constant numbers on the other side of the equation. Then, we must isolate the variable. Note, to check the solution, we plug the found value back into the equation and check that both sides of the equation get the same value. Doing this, we obtain: $$ 3x + 15 = 3x+15 \\ 15 =15 $$ This statement is always true, so we write it is true for all real numbers.