Может так 300 ???????
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<span>2х - 3ху + 7 - (3х - 5ху) = </span><span>2х - 3ху + 7 - 3х + 5ху = 2xy - x + 7</span>
3/8-1/7=21/56-8/56=13/56
11/80-11/90=990/7200-880/7200=100/7200
3/5-4/9=27/45-20/45=7/45
6-2 13/18= 5 18/18 - 2 13/18=3 5/18
23/25-11/15=69/75 - 55/75 =14/75
8 1/8 - 3 1/9=8 9/72 - 9 8/72=1 1/72
6 7/18 = 115/18
7,2=36/5
2,8=14/5
(71/4-115/18)*36/5+14/5=(639-230)/36*36/5+14/5=409/5+14/5=423/5=84.6
307145-29897=277248*26=7208448