i’m not quite sure what the question is but i’m guessing you need to simplify, if not lemme know and i’ll try help.
first combine the squared terms which is 1.5z^2+z^2= 2.5z^2
second combine the z terms
6z-3z=3z
then combine the numerical terms
4.5-0.3=4.2
so simplified that equation is
2.5z^2 + 3z + 4.2