Current Attempt in Progress

A large plate is fabricated from a steel alloy that has a plane strain fracture toughness of $84$MPa$\sqrt[\phantom{2}]{m}(76\mathrm{.}45$ksi$\sqrt[\phantom{2}]{10}).$ If the plate is exposed to a tensile stress of $363$MPa $(52650)$ during use, determine the minimum length of a surface crack that will lead to fracture. Assume a value of $1\mathrm{.}19$ for $Y.$

$mm$