(5а-4ab)/(ab-3b²) + (15b-12b²)/(3b²-ab) =
= (5a-4ab)/(ab-3b²) - (15b-12b²)/(ab-3b²) =
= ((5a-4ab)-(15b-12b²))/(ab-3b²) = (5a-4ab-15b+12b²)/(ab-3b²) =
= ((5a-15b)+(-4ab+12b²))/(ab-3b²) = (5(a-3b)-4b(a-3b))/(ab-3b²) =
= ((a-3b)(5-4b))/(b(a-3b)) = (5-4b)/b
(5-4b)/b = (5-4*500)/500 = (5(1-4*100))/500 = (1-400)/100 = (-399)/100 =
= -3,99
