add or subtract following polynomials

1.) (12y²+15y-20)+(8y²+10y+12)
2.) (-3a²-2a+7)+(4a²-5a-8)
3.) (10x²+12×+15)+(-6ײ+12×+4)
4.) (4b⁶-4b⁵)+(12b⁵-15b⁴+4)
5.) (-9ab²+1)+(7ab²+10b+3)
6.) (17×2+7×-14)-(-6×2-5×-18)
7.) (-18×2+4×-16)-(15×2+4×-13)
8.) (38m-27mn+44n2)-(52m2-46mn+59n2)
9.) (2×-23y)-(7×+5y-16z)
10.) (24×3-11×2+10×-42)-(17×2+4×-13)​