Answer
a. $23^{\circ}$ or $87 ^{\circ}$
Work Step by Step
$\sin{A}= \dfrac{a \sin{B}}{b} = \dfrac{28 \times \sin{35}}{19} = 0.845$
$A = 57.7^{\circ} \hspace{30pt} A' = 180 - A = 122.3^{\circ}$
$C = 180-(A+B) = 87.3^{\circ} \hspace{30pt} C' = 180-(A'+B) = 22.7^{\circ}$
