Simple questions on constraint optimization

[OggoTale]

Can anyone help me with (c)?

Answer:


How do we get this exactly, I understood how the conditions were reached but am not able to eliminate the variables some how?

This is from A.C. Chiang

[bear]

Put

1-y=-3-x
=>x-y= -4  .............(1)

From constraint, we know

x+y=6.....................(2)

Solve (1) and (2)