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Let the number of games played last year be y

This year they will play y-3

Total number of games they won last year = 80/100 x y = 0.8y

If they win 90% of their games this year they would have won 90/100 x (y-3) = 0.9y - 2.7

So 0.8y = 0.9y-2.7 since if they win 90% of their games this year,  they will have won the same amount of games as last year

Now lets solve

0.8y = 0.9y - 2.7

2.7 = 0.9y - 0.8y

2.7 = 0.1y

27 = y

y = 27

So this year they will play 27-3 = 24 games.