$6\mathrm{.}40$: For some metal alloy, a true stress of $315$ MPa produces a plastic true strain of $0\mathrm{.}02.$ How much will a specimen of this material elongate when a true stress of $415$ MPa is applied if the original length is $500mm?$ Assume a value of $0\mathrm{.}22$ for the strainhardening exponent $n.$