A cylindrical specimen of a metal alloy 51.3 mm long and 11.1 mm in diameter is stressed in tension. A true stress of 350 MPa causes the specimen to plastically elongate to a length of 57.9 mm. If it is known that the strain-hardening exponent for this alloy is 0.3, calculate the true stress (in MPa) necessary to plastically elongate a specimen of this same material from a length of 51.3 mm to a length of 60.5 mm.