4. Function properties: determine the properties (injective, surjective, bijective) of the following functions a. Let f :NN be defined by f(x) =x mod 12. b. Let f :R R be defined by f(x) =x/(x + 1). c. Let f :NNy defined by f(x)-3x mod 7. Hint: N7 means natural numbers less than 7 including 0