Let q be the number of weeks after the 5th week
We have this equation
total wins [ 2 + 2q ]
_________ = __________ = .50
total games [ 15 + 3q ]
Where n is the number of weeks after the 5th week
Multiply both sides by 15 + 3q and we have that
2 + 2q = .50 [15 + 3q ]
2 + 2q = 7.5 + 1.5q subtract 1.5n, 2 from both sides
.5q = 5.5 divide both sides by .5
q = 11
So..it will take 5 + q = n = 5 + 11 = 16 weeks to reach a 50% winning percentage
Proof:
After n = 16 weeks we have 2 + 2(11) = 24 wins
And 15 + 3(11) = 48 games will have been played
So
24 / 48 = .50