If x=6a+8b+9c;y=2b-3a-6c and z=c-b+3a ; find
(i) x+y+z (ii) x-y+z
(iii) 2x-y-3z (iv) 3y-2z-5x
3a−5z3b−5y=3a+5z3b+5y. Then, ab=zy