The yield strength for an alloy that has an average grain diameter of $5\mathrm{.}3{10}^{-2}mm$ is $123$ MPa $.$ At a grain diameter of $6\mathrm{.}7{10}^{-3}mm,$ the yield strength increases to $274$ MPa $.$ At what grain diameter, in mm $,$ will the yield strength be $246$ MPa $?$

$d=$ mm