1. 79/80-(3/16+39/60)=79/80-(180/960+624/960)=79/80-804/960=948/960-804/960=144/960=3/20
2. 2/45+(41/45-7/9)=2/45+(41/45-35/45)=2/45+6/45=8/45
3. 7/15-(2/15+1/5)=7/15-(2/15+3/15)=7/15-5/15=2/15
4. 3/16+(15/16-5/8)=3/16+(15/16-10/16)=3/16+5/16=8/16=1/2