Exercise concerning a joint pdf

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A joint pdf $f(x,y) = c(x+3y)$ with $0<x<1$ and $0<y<4$.

A) Determine $c$; B) Find the marginal pmf $g(x)$ and $h(y)$, C) Are $x$ and $y$ independent

My attempt:

  1. I set the double integral of $c(x+3y)$ equal to one and got $c=1/26$ but I'm a little shaky on my calculus.
  2. I had trouble here. I set $g(x)$ equal to the integral of $f(x)$ but got pretty confused trying to figure everything out.