7,2*2 1/12:(15 1/5-11 1/2) помогите!

7,2 * 2 1/12 : (15 1/5 - 11 1/2) =

1) 15 1/5 - 11 1/2 = 15 - 11 + 1/5 - 1/2 = 4 + 2/10 - 5/10 = 4 - 3/10 = 3 7/10;

2) 7,2 * 2 1/12 = 72/10 * (2 * 12 + 1)/12 = 72/10 * 25/12 = (12 * 6 * 5 * 5)/(5 * 2 * 12) = (6 * 5)/2 = 30/2 = 15;

3) 15 : 3 7/10 = 15 : 37/10 = 15 * 10/37 = 150/37 = 4 (150 - 148)/37 = 4 2/37.