The possible arguments of the functions f(x,y) and g(x,y)

The possible arguments of the functions f(x,y) and g(x,y) are x=0 or 1 and y = 0 or 1 and are defined by the following tables (Attachment) :

What is the value of f(a,b) + g(a,b) ?

(1)f(a,b) = 0
(2)g(a,b)= 0