Answer:
21=x
Step-by-step explanation:
Those angles will add up to 180.
So make your equation 180=3x-3+5x+15
Add like terms, so 3x+5x=8x and -3+15=12
Now you have 180=8x+12
Subtract 12 from both sides, leaving you with 168=8x
Divide by 8 on both sides.
21=x
