Converting an arithmetic function to a recursive one, using primitive recursion operators

Question

I need to convert this function to recursive: f(x,y) = 3x + y
If I convert through the primitive recursion operator, then I get like this:
f(x,0) = g(x) = 3x
f(x,y+1) = h(x,y,f(x,y)) = ???
But what to do next to get a recursive expression?