$22\mathrm{.}11$ A competitive firm uses two inputs and has a production function

f $($x$1$; x$2)=22$x$1^25.$ X$2^25$

The firm can buy as much of either factor as it likes at factor prices w$1=$ w$2=1.$ The cost of

producing y units of ouput for this firm is:

$($a$)2($y$/22)^2$

$.$

$($b$)22($x$1+$ x$2)$y$.$

$($c$)($x$1+$ x$2)/22.$

$($d$)$ y$/44.$

$($e$)$ y$^2/44.$