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We suspect that it's the first one, so let's explore the possibility. 

Let's try to figure it out logically. Okay, pi r squared is the area of an entire circle.     

Now it might not be good to start with an angle like, oh, 77^o for instance.  Hard to visualize.      

Pick an angle that's obvious, easy to visualize.  So, why don't we pick 180^o to start with.    

We know that 180^o represents half a circle, and 180/360 = 1/2 so that works out good.   

Try 90^o next.  That's obviously a fourth of a circle, and 90/360 = 1/4 so I think we can be confident. 

It's definitely the first one.      

 1)     A = n / 360° pi * r²              A = 90° / 360° * pi * 5²             A ≈  19.635 u²  

Number 2 works for   r = 1          A = n / 360° * pi * r         A = 90° / 360° * pi * 1        A ≈ 0.785 u°    

A = 360 / 360 * pi * 5²            A ≈ 78.539 u²