Can i play the sims 3 if i installed the sims 4

You can happily download both of these games to your Laptop if that's what you mean, the games are completely separate to each other and there is no reason why they cannot both be on your PC at the same time.
If you mean once you have bought and installed the Sims 4 can you automatically play the Sims 3 then no, you will have to go out and buy the Sims 3 game separate.