7x-5y=21 when x=4 from the coordinate point of (4,y) Next, 7x-5y=21 Substitute x with 4 7(4)-5y=21 28-5y=21 Add 5 to each side 28-5y+5y=21+5y 28=21+5y Subtract 21 to each side 28-21=21+5y-21 7=5y Divided 5 to each side 7/5=5y/5 y=7/5 Or y=1 2/5 Check: 7x-5y=21 Substitute x with 4 and y with 7/5 7(4)-5(7/5)=21 28-7=21 21=21. As a result, (4,7/5) is your correct answer. Hope it help!
If you know that x is 4, (assuming it's placed as x,y) then simply substitute 7(4)-5y=21. 28 - 5y =21. 28 - 21 =5y 5y= 5 Y= 1 Not sure if I'm right but I think that's how it's done the simple way.
