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The first step is to simplify the expression on either side of the equation:

x + 3 = 12.

Now, we solve as we did earlier:

Example 3

Solve the equation z - 6 = 5.

If we write

z = 5,

we've made the quantity on the left heavier by 6 but haven't made the quantity on the right heavier at all. Uh-oh—the scale's a-tippin'. To correctly solve the equation, we need to change each quantity by the same amount. We add 6 to the expression z - 6 and also add 6 to the expression 5 to get

z = 11

Example 4

Solve the equation 9 - 8 + 2 = x + 4.

First, simplify the expression on each side of the equation to find that