Question 452619
let d for adut, c for a child
 53 =7d+5c 
 9 = d+c
 9-d = c
sutitution c=9-d
53 =7d+5(9-d)
53 =7d+45-5d
53 = 2d +45
53-45 =2d
  8= 2d
 8/2=d
 4 = d
d+c =9
4+c=9
  c =9-4
  c =5