2*(500-y/3)=820
(500-y/3)=820/2
(500-y/3)=410
-у/3 = 410 - 500
-у/3 = -90
у/3=90
у=90*3
у=270
2*(500-у: 3)=820
(500-у:3)=820 : 2
(500-у:3)=410
-у:3=410-500
-у:3= - 90
у:3 = 90
2*(500-y/3)=820
(500-y/3)=820/2
(500-y/3)=410
-у/3 = 410 - 500
-у/3 = -90
у/3=90
у=90*3
у=270
2*(500-у: 3)=820
(500-у:3)=820 : 2
(500-у:3)=410
-у:3=410-500
-у:3= - 90
у:3 = 90
у=90*3
у=270