User:Jungcp

10. teacher A : 2h, teacher B : 1h $$ f(x) = \frac{2}{9}( 85 + 90 + x) + \frac{1}{9}(90+84+y) \geqq 90 $$

$$ 2( 85 + 90 + x) + (90+84+y) \geqq 810 $$

$$ y \geqq -2x + 461 $$

$$ x+y = k, maximum $$

$$ y = -x + k $$