John  averaged  82  out  of  100  on  his  first  three  tests.    what  was  john’s  score  on  the  fourth  test  if  his  average  after  the  fourth  test  dropped  to  79  out  of  100?     a)  cannot  be  found    b)  80      c)  75        d)  70  can somebody me with this question, i know the right answer is 70 but what i don't know is how to do it. asap.

answer: option a.

step-by-step explanation:

you know that the quadrilateral opqr ( a four sided figure) is inscribed in circle. this means that all its vertices are on the circle.

then, by definition, the opposite angles of the quadrilateral are supplementary, this means that the sum of their measures is 180 degrees.

you can observe in the figure that the angles ∠opq   and the angle ∠orq   are opposite, therefore:

then, can be used to d to calculate the measure of ∠opq