Please only answer using Mohr's circle

$1\mathrm{.}30.$ Using Mohr's circle, solve Prob. $1\mathrm{.}21.$

$1\mathrm{.}21.$ A welded plate carries the uniform biaxial tension illustrated in Fig. P$1\mathrm{.}21.$ Determine the maximum stress for two cases: $($a$)$ The weld has an allowable shear stress of $30$ MPa. $($b$)$ The weld has an allowable normal stress of$80$ MPa.

look at Figure P$1\mathrm{.}21$ shown below.