12-13,2:(3 11\21-2 4\15)
1) 74/21 - 34/15 = 740/210 - 476/210 = 264/210
2) 132/10 : 264/210 =132/10 * 210/264 = 21/2 = 10 1/2 = 10,5
3) 12 - 10,5 = 1,5