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 ?

What are the measures of angles a, b, and c? show your work and explain your answers. 25 points

Paula makes stained-glass windows and sells them to boutique stores. if her costs total $12,000 per year plus $4 per window for the frame. how many windows must she produce to earn a profit of at least $48,000 in one year if she sells the windows for $28 each? 1. define a variable for the situation. 2. write an inequality that represents her profit. note: revenue is money coming in. cost is money going out. profit is the difference between the revenue and the cost. in other words: revenue - costs profit 3.using words, describe how many windows she must sell to have a profit of at least $48,000.

1.3.4 practice : modeling: solving linear equations in this assignment, you may work alone, with a partner, or in a small group. discuss the results of your work and/or any lingering questions with your teacher. your assignment: road trip you're taking a scenic road trip down ca-highway 1 from san jose, california, to los angeles. you plan to split the drive into two days, stopping for one night. choose one town to stop in, and find the driving distance for the second day. 1. circle the town you chose to stop in. (1 point) santa barbara: an image of palm trees san luis obispo: an image of a church 2. why did you choose this town? (1 point) 3.what do you know? .what do you want to find out? .what kind of answer do you expect? define the variable. 4. what is the variable x for this problem? (1 point) write the equation. 5. write an equation showing that the distance traveled on the first day plus the distance traveled on the second day is equal to 425 miles. (4 points: 2 points for each side of the equation) isolate the variable. 6. what inverse operation do you need to perform on both sides to isolate x in the equation? (2 points: 1 point for the correct number, 1 point for the correct operation) solve the equation. 7. solve the equation for x. interpret the answer in terms of the problem. (2 points: 1 point for the solution, 1 point for the interpretation) check your solution. 8. to confirm that your answer is correct, add the two days' distances. this should equal the total distance from san jose to los angeles. show your work as an equation. (3 points: 1 point for the setup, 2 points for the correct answer)