8- 3/4=,12-5 7/9,6 2/5-4 3/5

8-3/4=8/1-3/4=(8х4)/1х4 - 3/4=(32-3)/4=29/4=7_1/4 или =7,25
12-5_7/9=12/1-52/9=(12х9)/1х9 -52/9=(108-52)/9=56/9=6_2/9
6_2/5-4_3/5=32/5-23/5=(32-23)/5=9/5=1_4/5 или =1,8