Question 83571
  
     Surface area of a cube  =  {{{6a^2}}}
     Here 'a' represents the length of the edge of the cube.
     Applying the same formula above, we get
     the answer = {{{6x^2}}}cms.
     Explanation:  A cube has got 6 sides and its sides are equal/congruent.
                   So the area of one side = {{{x^2}}}cms.
                   So 6 * {{{x^2}}} = {{{6x^2}}}cms.
     I hope this is clear to you.
     Coming to the second problem,
     Volume of a right cylinder = {{{height*pi*r^2}}}
     Again applying the above formula and the given data, we get
     Volume = {{{15.7x^2}}}cu.mtrs.  Answer.  
     i.e. {{{5*3.14*x^2}}}.  Here the value of pi has been taken as '3.14'
     I hope this too is clear to you.