Answer
$x=110,$ $y=220,$ $z=75$
Work Step by Step
Let $x$ be price for adult, $y$ be price for children and $z$ for senior citizen.
$\begin{cases}x+y+z=405\\
11x+6.5y+9z=3315\\
y=2x
\end{cases}$
replacing $y$ by $2x$ in equations, multiplying the first equation by $-8$ and adding it to the first equation.
$\begin{cases}-24x-8z=-3240\\
24x+9z=3315\\
-- -- -- --\\
z=75
\end{cases}$
$x=110,$ and $y=220$
