5·8·х - 5·1 - 7·4·х - 7·1 + 8·7 - 8·4·х = 9, 40·х - 5 - 28·х - 7 + 56 - 32·х = 9, -20·х + 44 = 9, -20·х = 9 - 44, -20·х = -35, х = -35:(-20), х = 1,75.
5·8·х - 5·1 - 7·4·х - 7·1 + 8·7 - 8·4·х = 9, 40·х - 5 - 28·х - 7 + 56 - 32·х = 9, -20·х + 44 = 9, -20·х = 9 - 44, -20·х = -35, х = -35:(-20), х = 1,75.