15 + 2x > 4x -7

get all the X's on one side and the numbers on the other.

Remember the four axioms of algebra:

equals added to equals are equal
equals subtracted from equals are equal
equals multiplied by equals are equal
equals divided by equals are equal

Simply add, subtract, multiply, or divide both sides of your equation by appropriate values until "x" remains alone on one side and a numeric value remains on the other side.

Start by adding 7 to both sides of the equation.