Find angle BPC
angle PBC = 150o which is the total of PBA (60o cuz the triangle is equilateral) plus ABC (90o cuz it says so)
since PBC is 150o that leaves 30o for the total of both BPC and BCP cuz the total of angles in a triangle is 180o
triangle PBC is isoceles since sides PB and BC are equal
therefore angles BPC and BCP are equal, so each one is half of their 30o total
so angle BPC is 15o cuz 15 is half of 30
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