Reference angle for -19pi/6?

i get confused whether to use one pi , or 2 pi , or 4 pi? i don't when to use it.
i understand how to sketch the angle , and find the degree of it but then i get lost with the radians.

my notes say the reference is 5pi/6 ? how did they get that ?

its a trick question

step-by-step explanation:

dogs love water, just turn on the hose and it will run in circles chasing the water all day : )

6(h+1)/2=a

a=area

step-by-step explanation:

its the same thing as a square or rectangle but after multiplying two sides you need to divide it by two.