You can put this solution on YOUR website! First expand the expression, by removing the brackets:
= -2(5x+z)-2(-5z-5x)
= -10x -2z + 10z +10x
Now collect the like terms (combine the x's with the x's and the z's with the z's):
= -10x+10x -2z+10z
= 0 + 8z
= 8z