Найдите значение выражения (1/6 + 1/10 + 1/15) : (3/5 - 1/3 - 1/4). полное решение.заранее !

1) 1/6 + 1/10 = 5/30 + 3/30 = 8/30 = 4/15!
2) 4/15 + 1/15 = 5/15 = 1/3
3) 3/5 - 1/3  = 9/15 - 5/15 = 4/15
4) 4/15 - 1/4 = 16/60 - 15/60 = 1/60
5) 1/3 : 1/60 = 1/3 * 60 = 20

(5/30+3/30+2/30):(36/60+20/60+15/60)=
10/30:1/60=
20