Explain how to solve 2x + 7 = 15

You would work backwards:15-7=8, because you will be adding this anyways later, and then you see that 2x = 8, then divide both sides by two, and you are left with the equation: x = 4, and there is your answer. x = 4.

The x would be 4 because if you multiply 2 times 4, that's 8, and 8+7=15