A sample of austenite $($gamma$-$Fe$),$ see phase diagram below, is produced and taken to XRD$.$

Given a lattice parameter $($a$)$ of $3\mathrm{.}57,$ what angle of $2-$theta $($in degrees$)$ would you expect the first XRD peak to be located at if Cu $($lambda $=1\mathrm{.}54)$ was used as the X $-$ray source? $($one decimal place$)$