HI could someone help me with this question? Thank you very much

A tip: Just solve & solve it, you will end up having solution.

At first,

On comparing, we can say that,

Put e = f - 10 in 4e = 9f

Put f = -8 in equation(i) to find the value of e;

And finally we have got f = -8 & e = -18, now let procede futher;

Thus, our final answer is 180.

the arc length is found by finding the circumference of the full circle (2xpixradius) and then dividing by 4 to find just one quarter of the circle (90 degrees).