One type of steel has density  $7800kg/m^3$ and will break if the tensile stress exceeds  ${\text{7.0\hspace{0.17em}×10}}^{\text{8}}{\text{N/m}}^2$. You want to make a guitar string  using 4.0g of this type of steel. While in use, the guitar string must be able to withstand a tension of  900N without breaking. Determine the maximum length the string can have (in m)