Question 1039399
<pre>
  1. ~H &#8744; F 
  2. F &#8594; J 
  3. ~~H       &#8756; ~F &#8744; J 
  4. F           1,3, Disjunctive syllogism 
  5. J           2,4, Modus ponens  
5.5. J &#8744; ~F        5, Addition
  6. ~F &#8744; J      5.5, Commutation.  

[Notice I put in an extra step, numbered 5.5.  Maybe 
your professor considers ~F &#8744; J and J &#8744;~F to be to 
same without bothering with commutation.  

Edwin</pre>