The quadratic formula is -b + or - the square root of b squared - 4 times the a value and c value over 2a. So the roots would be -1.354249 and -6.645751. I believe these are the roots.
Observe the given figure.
Here, angle T and R are the inscribed angles.
And sum of inscribed angles is half of measure of intercepted arcs.
Since, the measure of intercepted arcs is 360 degrees.
Therefore, 

Hence, the sum of the two angles is 180 degrees.
Therefore, these are the supplementary angles.
Therefore, angle T and angle R are supplementary angles.
Hence, proved.
Line 3
since he added which is against the order of opreation rule he was supposed to multiply first then add
again what he was supposed to do is
Line 2:21+5+6(2)
Line 3:21+5+12
I think it’s b... I don’t but i tried if it is wrong I’m sorry if it was right your welcome