19) you have to look for similar terms
you can see there is more than one term with y^2 in it
-3y^2 - 5y^2
= -8y^2
there is also more than one 'z' term
3z-5z = -2z
dont forget about the 4x^2 and put it together
answer = 4x^2 - 8y^2 - 2z
i think you got confused because of the way you laid out your working??
next time identify the like terms and try working them out seperately first
