In f = {(a,b), (c,d), ...} by definition f(a) = b, f(c) = d... In short the first element of the pair goes to the second element.
(a) So f(2) = 3.
(b) g-1 is not a function as g-1 = {(1,2),(1,3),(2,4)}. So 1 goes to both 2 and 3 which is not allowed for a function.
(c) fog means composition of f and g. Start with g and notice where it sends each element. Then wherever the element has been sent it is further operated upon by f. For example 2--->1 by g and then 1--->2 by f. So in the combined action of fog 2--->2. Hence fog sends 2 to 2, 3 to 2 and 4 to 3. So fog = {(2,2),(3,2),(4,3)}.