Josephine is taking a college course, and her professor bases the course grade on the average of 2 tests taken in the semester. She wants to know what she needs to earn on the last test to maintain her grade. Rearrange the following equation for b, where C is the average of 2 test scores, a and b.

C equals the quantity a plus b all over two

b equals two times C over a
b = 2C + a
b = 2C − a
b = 2C(a)