Answer:
Step-by-step explanation:
3x and 3y are not "like terms," despite having the same coefficient.
Like terms have the same variable. For example, 3x and 2x are like terms, so
3x+2x = 5x
Answer:

Step-by-step explanation:


15x+10x=12x+90; ⇔ 13x=90;

Answer:
18.84
Step-by-step explanation: