Rewrite the equation using the given numbers for A and B. For this example, the equation is X + A = B, where A= 5 and B = 9. Rewritten, the equation is X + 5 = 9. X in this equation is known as the variable.
Subtract the same amount from each side of the equation so that X (the variable) is on one side of the equation and the known numbers are on the other side.
For our example: X + 5 - 5 = 9 - 5. Working the math, the equation now reads X = 4.
Replace X with your answer in the original algebraic equation to see if the solution is correct. X + 5 = 9, where X = 4 is rewritten 4 + 5 = 9. Because 4 + 5 does equal 9, you can be sure you found the correct X factor for this equation.