[(6,6 - 3 3/14) * 5 5/6] : [(21 - 1,25) : 2,5] = 2,5
1) 6,6 - 3 3/14 = 6 6/10 - 3 3/14 = 6 42/70 - 3 15/70 = 3 27/70
2) 3 27/70 * 5 5/6 = 237/70 * 35/6 = 237/12 = 19 9/12 = 19 3/4 = 19,75
3) 21 - 1,25 = 19,75
4) 19,75 : 2,5 = 7,9
5) 19,75 : 7,9 = 2,5