1.9 - (5 3/4 - (x+1)) = 3.15

1,9 - (5_3/4 - (х+1)) = 3,15

19/10 - (23/4 - (х+1)) = 315/100

- (23/4-х-1) = 315/100-19/10

х+1-23/4 = (315-190) / 100

х=125/100-1+23/4

х = (125-100+575) / 100

х=600/100

х=6

или

1,9 - (5_3/4 - (х+1)) = 3,15

1,9 - (23/4 - (х+1)) + 3,15

1,9 - (5,75-х-1) = 3,15

1,9-5,75+х+1=3,15

х=3,15-1,9+5,75-1

х=6