Find x.
circle s with inscribed triangle pqr, side pr goes through point s, side pq is congruent to side qr, angle p equals x minus 10 degrees, angle r equals 2 x plus 10 degrees

(x+10) = (2x-25) - (as the two lines on the triangle symbolises the two equal sides and angles)
Now just substitute it, to get x:
10 = x - 25 - (to bring x to the right hand side, you have to minus it from 2x)
35[degrees]= x - ( to gather the like terms, add 25 to 10, to get your final answer)
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To prove this is correct, add up all the angles and see if it equals 180 degrees:
(x+10)+(2x-25)+90 = 180
45 + 45 + 90 = 180
180 = 180,
So x does equal 35 degrees.

If in any case you don’t understand my working out, please tell me so I can explain it better!