Answer:
9x²+9y²-x
Explanation:
Combining like terms
-9x is a different term than 9x^2 however 9x is like terms with x. Coefficients really are the only thing that are excused for like terms
Now with that out of the way,
1 - Rewrite
9x²+3y²+6y²-x
This step becomes more useful as you go on in algebra as organization will soon start to correlate how fast you complete problems correctly
2 - Find like terms
9x² does not have any like terms
+3y² is like terms with +6y²
-x does not have a like term
3 - Combine like terms
9x²+(3y²+6y²)-x
↓
9x²+9y²-x
Hope this helps :)