[will mark as brainliest] can someone me understand this and me get the answer?

The intersecting tangents theorem says that the measure of angle PQR is half the difference of the measures of the arcs that the tangents intercept. This means

where refers to the major arc PR, and refers to the minor arc PR (the one you know has measure ).

The major and minor arcs PR form the circle, so their measures add up to 360º:

Then by the aforementioned theorem, we have

Then the minor arc PR has measure 100º, making the answer A.

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step-by-step explanation: