5\6*9\15-5\12*4\15, 7\18*9\14-5\12*4\15, 9\20*2\3+5\14*7\25,

1) 5/6 * 9/15  -  5/12*4/15 =
= (5*9) / (6*15)  -  (5*4)/ (12*15)=
= (1*3) / (2*3)  -  (1*1) /(3*3)=
= 1/2 - 1/9= 9/18- 2/18 = 7/18
2) 7/18*9/14 -  5/12*4/15=
= (7*9)/(18*14) - (5*4) / (12*15)=
= (1*1)/( 2*2) - (1*1)/ (3*3)=
=1/4-1/9 = 9/36 - 4/36 = 5/36
3) 9/20*2/3  +  5/14*7/25=
= (9*2)/ (20*3) + (5*7)/(14*25)=
= (3*1)/ (10*1) + (1*1)/(2*5) =
= 3/10 + 1/10 = 4/10= 2/5