Look again at your equation. The 3 in front of the parentheses means that you have to multiply 3 times anything inside the parentheses. That is the distributive property.

Let's see how it works:

5x + 3(x + 4) = 28 Multiply 3 times x and 3 times +4, and remove the parentheses

5x + 3x + 12 = 28

Now add the 5x and 3x terms:

8x + 12 = 28

Subtract 12 from both sides:

8x = 16

Now divide both sides by 8 to leave a single x on the left:

x = 2

This is your solution. Check it by plugging 2 in for each x in the original: