Question

how do you graph 80x+40y=400 and 20x+80y=420

Answer 1

set x = 0 in first equation, 40y =400 so y = 10 mark the point (0,10)
set y= 0 in first equation, 80x = 400 so x = 5 mark the point (5, 0)
Join the two points with a straight line

Do same for second equation.

Answer 2

20x=420so x =21

Answer 3

80y=420 is (0,5.25)