start by combining like terms
x + 3x = ?
1x + 3x is what? (its just 1+3 because the x makes it where 1x and 3x are equal.)
We cannot just give you the answer. You need to work for it. Got it? If you try, you can do this.
I thought it was 4
almost hint: 1 + 3 = 4 x + 3x = __ fill in the blank
Yes! so 4x + 5 = 21. Subtract 5. 4x + 5 - 5 = 21 - 5 what is 5-5? what is 21-5?
The answer is $ but start by combining like terms so its x + 3x +4x but 21 - 5 4x = 16 4x/16 = 4