Question 7
Given four integers $a,b,c,d$, form another four new numbers, where each new number is obtained by adding to each of $a,b,c,d$ the average of the other three integers. In other words, add to $a$ the average of $b,c,d$ to form a new number; add to $b$ the average of $a,c,d$ to form another new number, and so on. If the four new numbers formed are $28,37,46,$ and $57$, find the average of $a,b,c,d$.