Question 414864
suppose, nick has  x dollars

==> John has   x + 13

so the total is,  x + x+ 13 = 81

==> 2x + 13 = 81

==> 2x+ 13 -13  = 81-13

==>  2x = 68

==> {{{2x/2  = 68/2}}}

==>  x = 34

==> Nick has 34 dollars...

so john has 34 + 13 = 47 dollars...