Question

3b(x-y)+(x-y)+(x-y)=3(x-y)×(3b+1)

Answer 1

3b(x-y)+x-y=3bx-3by+x-y=(3bx+x)-(3by+y)=x(3b+1)-y(3b+1)=(x-y)(3b+1)

Answer 2

легко и просто