Let N denote the natural numbers. Let f: NxN -> N be defined by

f(a,0) = a for all natural numbers a

f(0,b) = 2b for all natural number b

f(a,b) = [f(a-1, b) + f(a, b-1)+3]/2 for all positive integers a,b

Compute f(a,b) for all 0 <= a,b <= 3

Prove that f(a,b)<= 2(a+b) for all natural numbers a,b by induction

Any guidance and help is much appreciated I am not sure where to begin with this problem. Thank you.