This expression contains two types of different terms, those that contain(p^2) and those that contain p. p2 and p are not like terms because although they contain the same letter, the letters do not have the same power.

2(p^2)+3p+(p^2)

2(p^2)+(p^2)\=3(p^2)

+3p

Putting the simplified terms together gives 3p2+3p