[tex]\displaystyle \frac{A}{4} = \frac{B}{5} = \frac{C}{3} = \frac{180}{4+5+3} = \frac{180}{12} =15 \\ \\ A=4 \cdot 15=60^o \\ B=5 \cdot 15=75^o \\ C=3 \cdot 15=45^o \\ m(\ \textless \ A)=60+45=105^o \\ m(\ \textless \ B)=75^o \\ m(\ \textless \ D)=m(\ \textless \ C)=45^o+45^o=90^0[/tex]