Helpppp

Note that, using the change-of-base theorem  we can write

y =  [ log r / log 2 ]  * [ log r / log 4 ]

y  =  ( 1  / [ log 2 *log 4 ])  * [ log r ] ^2       

Note  that  ( 1 / [ log 2 * log 4] )  is a constant

Apply the chain rule  to   [ log r ] ^2

Remember  that the derivative  of log r   =  1 / r

y ' =   ( 1/ [ log 2 * log 4]  *  2 * [ log r ] *  [ 1/r]        

               2  log r

y '  =    _____________

         r [ log 2 * log 4 ]