They’ve already played 20 games and there are 40 remaining, so 60 total games.
80 * .625 = 37.5, so they need to win at least 38 games to make the playoffs. So they must win 30 more games. If they do so they’ll have won 38 out of 60. Winning 2 games out of 5 in the playoffs means their total is 40 out of 65. 40/65 = .6153 = 61.5%.