Let the total money all the brothers have be $x.
It was given that Peter's money is 20% of the total money. This means that Peter's money will be:
[tex]\Rightarrow\frac{20}{100}\times x=0.2x[/tex]It is also given that Peter's money is $8.00. Therefore, we have that:
[tex]0.2x=8[/tex]Solving, we can get the value of x to be:
[tex]\begin{gathered} x=\frac{8}{0.2} \\ x=40 \end{gathered}[/tex]Therefore, they all have a combined amount of $40.00.
OPTION C is the correct option.