(a). f(0) = 1

(b). DNE because there is a gap in the graph when x = 0. The "one-sided" limits are not equal (the limit from the left of f(x) as x approaches 0 is 4 while the limit from the right of f(x) as x approaches 0 is 1).

(c). f(3) DNE

(d). As x approaches 3 from the left and from the right, f(x) approaches 4. So the limit is 4.