6целых 7/12 плюс (5целых 3/40 минус 4целых 8/18)​

6 7/12 + (5 3/40 - 4 8/15) = 79/12 + (203/40 - 64/15) = 79/12 + (3045/600 - 2560/600) = 79/12 + 485/600 = 79/12 + 97/120 = 790/120 - 97/120 = 693/120 = 231/40 = 5  31/40

1)0.28*х*0.35х=980

0.098х*х=980

х*х=10000

х=100

х=-100

2)5х/12*0.72х=480

0.3х*х=480

х*х=1600

х=40

х=-40