вычислите 3/10-9/25:(4-1 9/10)+4/7

1) 4 - 1 9/10 = 3 10/10 - 1 9/10 = 2 1/10   
2) 9/25 : 2 1/10 = 9/25 * 10/21 = 6/35   
3) 3/10 - 6/35 = 21/70 - 12/70 = 9/70   
4) 9/70 + 4/7 = 9/70 + 40/70 = 49/70 = 7/10 = 0,7