selmash21 3.
108÷9/7=108×7/9=84

4.
8/24х+6/24х+3/24х=34/45
17/24х=34/45
х=34/45÷17/24
х=34/45×24/17
х=16/15=1 1/15

5.
11.25+4.3=15.55=15 11/20
15 11/20-3 5/12-7 19/30=
=15 33/60-3 25/60-7 38/60=
=14 93/60-3 25/60-7 38/60=
=4 30/60=4 1/2
7 7/12-5 5/6=6 19/12-5 10/12=
=1 9/12=1 3/4
4 1/2÷1 3/4=9/2÷7/4=
=9/2×4/7=18/7=2 4/€