Izzie recently took a math test where each correct answer (a) on the main part of the test was worth 6.1 points. She also correctly solved a bonus question worth 13 points. Using the equation 6.1a + 13 = 80.1, how many correct answers (a) did Izzie have on the main part of the test?

A.
11
B.
12
C.
15
D.
78