The sum of all three angles of a triangle is 180 degrees. Here we know two of these angles immediately: 65 and 51 degrees. The third is 180 - (65 + 51), degrees, or 64 degrees.
Angle PST and this 64 degree angle form straight angles; their sum is 180 degrees. We are to find Angle PST. Do that by subtracting 64 from 180:
The angles of any triangle will add up to 180°. Since we know the measures of ∠SPR and ∠PRS, we can find the measure of ∠PSR by adding the two measures and subtracting from 180°.
Now we know the measure of ∠PSR. Note that ∠PSR is supplementary to ∠PST, meaning that both values add up to 180. Let's do the math then.
