Use the given diagrams to calculate the unknown variables, specifically for Exercise 3, page 217, part a).

Here are the calculations for the unknown variables in the given diagrams.

** PAGE 217**

a)

Step 1: Identify the relationship between $\angle PQR$ and $\angle POR$.
$\angle PQR$ ($x$) is an angle at the circumference subtended by arc PR. $\angle POR$ ($55^\circ$) is the angle at the center subtended by the same arc PR.

Step 2: Apply the theorem that the angle at the center is twice the angle at the circumference.

$$x = \frac{1}{2} \times \angle POR$$ $$x = \frac{1}{2} \times 55^\circ$$ $$$$