3/8+2/15+х=90 с дробями
45/120+16/120+х=90 61/120+х=90 х=90-61/120 х=89ц59/120
http://znanija.com/task/20576258
3/8 + 2/15 + x = 90 x = 90 - 3/8 - 2/15 x = 90 - 45/120 - 16/120 x = 90 - 61/120 x = 89 целых 59/120