Add, Then Divide

In $4x-7 = 9$, the unknown is multiplied by 4, and then 7 is subtracted. Undo the subtraction first by adding 7 to both sides. Then divide both sides by 4:

$$4x = 16$$

$$x = 4$$

Check: $4\cdot 4-7 = 9$, which is true.

The sign in front of a number is part of that number. In $4x-7$, the second operation is minus 7, and the inverse of minus 7 is plus 7. If you read it as 7 and subtract, you get $4x = 2$ and a wrong answer. Checking the answer in the original equation shows the mistake.