12*(одна целая 3/4х+5/8)=восемь целых 1/2

12 *(1 3/4 х + 5/8) = 8 1/212 *(7/4 х +5/8) = 8 1/221х + 60/8 = 17/221х = 17/2 - 60/821х = 68/8 - 60/821х = 1х = 1/21

12*(7/4х + 5/8)= 17/2, 21х+ 15/2-17/2 = 0, 21х = 17/2-15/2, 21х = 1, х = 1/21.