Current Attempt in Progress

The yield strength for an alloy that has an average grain diameter of $5\mathrm{.}1{10}^{-2}mm$ is $133$ MPa $.$ At a grain diameter of $7\mathrm{.}4{10}^{-3}mm,$ the yield strength increases to $230$ MPa $.$ At what grain diameter, in mm $,$ will the yield strength be $232$ MPa $?$

$d=$ mm