The yield strength for an alloy that has an average grain diameter of $4\mathrm{.}8{10}^{-2}mm$ is $129$ MPa $.$ At a grain diameter of $7\mathrm{.}3{10}^{-3}mm,$

the yield strength increases to $276$ MPa $.$ At what grain diameter, in mm $,$ will the yield strength be $240$ MPa $?$

The yield strength for an alloy that has an average grain diameter of $4\mathrm{.}8{10}^{-2}mm$ is $129$ MPa $.$ At a grain diameter of $7\mathrm{.}3{10}^{-3}mm,$

the yield strength increases to $276$ MPa $.$ At what grain diameter, in mm $,$ will the yield strength be $240$ MPa $?$