Can someone explain how i do these ?

Use circumcenter theorem to solve for the given values

Type the correct answer in the box. consider the system of linear equations below. rewrite one of the two equations above in the form ax + by = c, where a, b, and c are constants, so that the sum of the new equation and the unchanged equation from the original system results in an equation in one variable.

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