1)(8 + 3x) (2 y - 1)=8*2y-8+3x*2y-3x = 16y-8+6xy-3x

2)3a-3c+xa+xc = 3a-3c +ax +cx

3)6x+7y+42+xy = 6(x+7)+y(7+x)= (x+7)(6+y)

4)ab-ac-4b+4c = a (b-c)-4(b-c)= (b-c)(a-4)