Answer:
1.) (18x-4y+12) - (2x-7y+10)
= (18x-4y+12) + (-2x+7y-10)
= 16x+3y+2
2.) (a²b+3a-5) - (7a-2b+7)
= (a²b+3a-5) + (-7a+2b-7)
= a²b-4a+2b-12
3.) (10g-7h) - (-12g+3h-9)
= (10g-7h) + (12g-3h+9)
= 22g-10h+9
4.) (x²+y²-3x+4y) - (4x²+y²-7x+2)
= (x²+y²-3x+4y) + (-4x²-y²+7x-2)
= -3x²+4x+4y-2
5.) (15k²+3k-8) - (7k²-9k+10)
= (15k²+3k-8) + (-7k²+9k-10)
= 8k²+12k-18
