Let x be the (unknown) number.


First sentence is translated into this expression  3*(x+15).


Second sentence is translated into this expression  5*(x-4).


These numbers are the same, so we write equation

    3*(x+15) = 5*(x-4).


Then we solve equation using standard procedures

    3x + 45 = 5x - 20

    45 + 20 = 5x - 3x

      65    =    2x

       x    =    65/2 = 32.5.


ANSWER.  The number is 32.5.


CHECK.  You can easily check that 3(x+5) = 3*(32.5+5) = 142.5 is the same 

        as 3*(x-4) = 3*(32.5-4) = 142.5.    It confirms the answer.