m+2n-3p
=3a^3-10a^2-5+2(-2a^3+5-10a)-3(7-5a-2a^2)
=3a^3-10a^2-5-4a^3+10-20a-21+15a+6a^2
=-a^3-4a^2-5a-16


m-3n+2p
=3a^3-10a^2-5-3(-2a^3+5-10a)+2(7-5a-2a^2)
=3a^3-10a^2-5+6a^3-15+30a+14-10a-4a^2
=9a^3-14a^2+20a-6