Cylindrical specimen of a metal alloy 46.0 mm long and 9.72 mm in diameter is stressed in tension. A true stress of 386 MPa causes the specimen to plastically elongate to a length of 52.9 mm. If it is known that the strain-hardening exponent for this alloy is 0.2, calculate the true stress (in MPa) necessary to plastically elongate a specimen of this same material from a length of 46.0 mm to a length of 55.6 mm.