1) 11x-11y= 11(x-y)
2) y(a+b)-7(а+b)= (a+b)(y-7)
3) 4a+4c-m(a+c)= 4(a+c)-m(a+c)=(a+c)(4-m)
4) ax-ay+12x-12y=ax+12x-ay-12y=x(a+12)-y(a+12)=(a+12)(x-y)
