For a rough calculation (which would assume an equal number of credits each year), try:
(3.0 + 4.0*3)/4 = 3.75
So in order to get a 3.8, your 'friend' will have to take more credits than they took freshman year, and do better in all of them.
Fortunately, a 3.8 is in no way necessary for MD matriculation 😉