3/10-9/25:(4-1 9/10)*4/7
Это дроби

3/10 - 9/25 : (4 - 1 9/10) * 4/7 = 99/490,1) 4 - 1 9/10 = 3 10/10 - 1 9/10 = 2 1/10,2) 9/25 : 2 1/10 = 9/25 : 21/10 = 9/25 * 10/21 = 6/35,3) 6/35 * 4/7 = 24/245,4) 3/10 - 24/245 = 147/490 - 48/490 = 99/490