for this case we have that $ 4 represents 20% of the price of the video game. Let "x" be the variable that represents the price of the game, so we make a rule of three:
4$ ----------> 20%
x -------------> 100%

Thus, the video game costs $20. Of those $20, $4 are from Peter, then his 4 brothers combined $16.
Among the 5 brothers combined $20
ANswer:
$20