Explanation:
If the whole bar is equal to 320 and you are given the numbers and variables, what would the equation be? Well, the line above the bar AND the bar are equal to each other. This means that the ORIGINAL EQUATION WILL BE: 4x + 12x = 320 (this will be your first answer).
Because 12x and 4x are LIKE TERMS, you can simplify them by adding them together like so: 12x + 4x = 16x. Now you can say that 16x is equal to 320 (this is your second answer).
Divide both sides by 16 to get the true value of ONE x. Like so:
16x / 16 = 320 / 16
x = 20 (this is your third answer)