Answer: D) 55.7 degrees approximately
=====================================================
The reference angle has AC = 12.3 as the opposite side and BC = 8.4 as the adjacent side. The tangent ratio ties the opposite and adjacent sides together.
--------
tan(angle) = opposite/adjacent
tan(theta) = AC/BC
tan(theta) = 12.3/8.4
theta = arctan(12.3/8.4)
theta = 55.6697828044967
theta = 55.7 degrees approximately
--------
arctan is the same as inverse tangent which is written as
make sure your calculator is in degree mode