F.2 Math急急!!!!!!!

1)
3a-2ab+6a^2-b
=3a+6a^2-2ab-b
=3a(1+2a)-b(1+2a)
=(1+2a)(3a-b)
2)
Since 3(8)+4(-3)-12=0
Hence the point (8,-3) is on the straight line 3x+4y-12=0
3)
A= (a+b)h/2
2A=(a+b)h
2A/h=a+b
b=(2A/h)-a