I need help on this math question

When you are making a circle graph by hand, how do you convert a number for a part into its corresponding angle measure in the circle graph? when you are making a circle graph by hand, what should you do if one of your angle measures is greater than 180°?

This is so hard and it’s for a test

If t8 = 4 and t12 = −2, find the first three terms of the arithmetic sequence.