Solve for x: 2x+5=21
Notice that 2 is "closest" to variable x, and 5 is "farthest" away. This simple observation allows us to decide which number to eliminate first. It is obviously +5 because it is farther between the two. The opposite of +5 is -5, so that means we will subtract both sides of the equation by 5.
Now it's time to get rid of the number closest or directly attached to x which is 2. Since +2 is multiplying the variable x, its opposite operation is to divide by 2.