Answer
$$4a^3-3a^2-5a.$$
Work Step by Step
We simplify by adding the $a^3$-terms as follows
$$3a^3+a^3=4a^3,$$
adding the $a^2$-terms,
$$2a^2-5a^2=-3a^2$$
adding the $a$-terms,
$$-7a+4a-2a=-5a$$
adding the constant terms,
$$5-2-3=0$$
The result is
$$4a^3-3a^2-5a.$$
