20000=.3(28x+36y)-65000 and x+y=10000

20000=.3(28x+36y)-65000 and x+y=10000

Using x + y = 10000      subtract x from both sides....so y = 10000 - x.....and substituting this into the first equation, we have

20000 = .3(28x + 36(10000-x)) - 65000

20000 = .3(28x + 360000 - 36x) - 65000

20000 = .3(360000 - 8x) - 65000

20000 = 108000 - 2.4x - 65000

20000 = 43000 - 2.4x    subtraact 43000 from both sides

-23000 = -2.4x              divide both sides by -2.4

x = about 9583.33

So y =10000 - x =   10000 - 9583.33 = about 416.66