Letters a, b, c, and d are angle measures. Lines f and g are intersected by line n. At the intersection of lines n and g, clockwise from the top, the angles are: a, 75 degrees, blank, b. At the intersection of lines n and f, clockwise from the top, the angles are blank, blank, d, c.

Which should equal 105° to prove that f ∥ g?

a
b
c
d