Question

Find the unknown marked angle

Answer 1

Find $b$

${121}^{\circ }+{43}^{\circ }+a={180}^{\circ }$(Pair of adjacent angles of a parallelogram are supplementary)

$$\begin{gathered} {121}^{\circ }+{43}^{\circ }+a={180}^{\circ } \\ {164}^{\circ }+a={180}^{\circ } \\ a={180}^{\circ }-{164}^{\circ } \\ a={16}^{\circ } \end{gathered}$$

so $a={16}^{\circ }$

Hence, $a={16}^{\circ }$