1÷(5/7)+()×(2/5)=3/2
===> (7/5)+()×(2/5)=3/2
===> 14+4()=15
===> ()=1/4
(3/4)×[()+(1/3)]÷(1/3)=2
===> (9/4)×[()+(1/3)]=2
===> ()+(1/3)=2×(4/9)=8/9
===> ()=(8/9)-(1/3)
===> ()=5/9
7x÷(2/3)=14
===> 7x×(3/2)=14
===> (21/2)x=14
===> x=14×(2/21)
===> x=4/3
(13/12)x=18×(13/24)
===> x=18×(13/24)×(12/13)
===> x=9
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