How to calculate orbital period with perihelion and aphelion?

By  the  use  of  kepers   3rd  law  which   state  that  the   square  of  the   orbital  period   is  proportional   to  the  cube  of  the  average  distance  from  the  sun.
that  is  T^2   is  proportional to R^3  
write  the  above as  ratio  with  constant  c  since  the  ratio  is  the  same  for  any  body  that  orbit the  sun
by  rearranging the  expression  we  get  T^2=cR^3(formula  of  calculating  the orbital  period
N.b  c  is  calculated  by  finding  the  average  of perihen  and  aphelion

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The answer is as follows in the photo