I submitted it and got a 19/20! Thanks everyone!

I've been trying to do these for a while and just can't figure them out. I've asked my parents, but they don't know either, soI asked my teacher and they told me to just use the equation, which I have been doing, so that was no help.

Formula is:
L = (n/360)(2(PI)r)

Where:
L = Length, n = degree measure of arc, r = radius of the circle.

In these questions I need to find the arc length.

11. r=10 n=20

A) 15(pi)/ 7
B) 13(pi)/ 5
C) 16(pi)/ 2
D) 11(pi)/ 4
E) 10(pi)/ 9
F) 9(pi)/ 4

So, I set up the equation L = (20/360)(2(PI)10). Then I reduced the first part, L = (1/18)(20(PI)). So the answer would be 20(PI)/18? I'm just so lost on this.

Other Questions That are Similar That I Don't Understand:

12. r=3 n=6

A) pi/9
B) pi/12
C) pi/26
D) pi/10
E) pi/8
F) pi/4

13. r=4 n=7

A) 8(pi)/55
B) 6(pi)/12
C) 7(pi)/45
D) 2(pi)/22
E) 9(pi)/18
F) 7(pi)/37

14. r=2 n=x

A) x(pi)/15
B) x(pi)/30
C) x(pi)/60
D) x(pi)/90
E) x(pi)/120
F) x(pi)/150

Then, how would you find the radius if:

16. n=30 L=1/3xy(pi)

A) 6xy
B) 8xy
C) 2xy
D) 10xy
E) 3xy
F) 14xy

I don't know how to do this one at all.