Answer:
1. 8x + 3y - x - 2y
= 8x - x + 3y - 2y
= 7x + y
2. 3n - 7n - 2n + x + 8x
= 3n - 9n + 9x
= - 6n + 9x
3. 2r - 5n + 9y - 3r + n
= 2r - 3r - 5n + n + 9y
= -r - 4n + 9y
4. 12y - 6x + 5y - 3n
= 12y + 5y - 6x - 3n
= 17y - 9n
5. - 13n + 4n - r
= -9n - r
6. 7xy - 8x + 6xy - y
= 7xy + 6xy - 8x - y
= 13xy - 8x - y
7. - 14r - 10n - 3r - 9n
= -14r - 3r - 10n - 9n
= - 17r - 19n
8. 6r + 9r - 2r - 13n
= 6r + 7r - 13n
= 13r - 13n
9. n + r + x - 3x +4r
= n + r + 4r + x - 3x
= n + 5r - 2x
10. 15y - 7x + 9z + 4z - 3x
= 15y - 7x - 3x + 9z + 4z
= 15y - 10x + 13z
Explanation:
You just have to group like terms and then 'add' or 'subtract'.