Answer
See answer below.
Work Step by Step
a. Domain : The set of all $(x,y)$ when $y -x \geq 0 \implies y \geq x$.
b. Range is given as: $z\geq 0$
c. Level Curves: These are straight lines $y-x=c$ and parallel to the line $y=x$
d. Boundary point is $\sqrt {y-x} =0$ and a straight line such as $y=x$
e. Closed
f. Unbounded
