Given:
The exterior angle P is 74°
The measure of ∠PRQ is 51°
We need to determine the measure of ∠PQR
Measure of ∠QPR:
From the figure, it is obvious that P is the intersection of the two lines.
The angle 74° and ∠QPR are vertically opposite angles.
Since, vertically opposite angles are always equal, then the measure of ∠QPR is 74°
Thus, the measure of ∠QPR is 74°
Measure of ∠PQR:
The measure of ∠PQR can be determined using the triangle sum property.
Thus, we have;
![\angle PQR+\angle QPR+\angle PRQ=180^(\circ)](https://img.qammunity.org/2021/formulas/mathematics/college/yls0et6xjzu7ro0rjijg7cozyanp1yjbys.png)
Substituting the values, we get;
![\angle PQR+74^(\circ)+51^(\circ)=180^(\circ)](https://img.qammunity.org/2021/formulas/mathematics/college/p7b5okhm1tzfqn2kilvs0owagrd6gxhuu7.png)
![\angle PQR+125^(\circ)=180^(\circ)](https://img.qammunity.org/2021/formulas/mathematics/college/apw269qw12ubb3ej1amwwg4vmdl5uhxh8g.png)
![\angle PQR=55^(\circ)](https://img.qammunity.org/2021/formulas/mathematics/college/3zehbeh76j7kevf9wh2v475p1qxf7jawoz.png)
Thus, the measure of ∠PQR is 55°
Hence, Option B is the correct answer.