Explanation:
Angle E is 90 degrees. The segment DC = 53 is opposite this angle. Note how "DC" does not contain the letter "E". Furthermore, note how this is the largest side. So it's the hypotenuse.
The side ED = 28 is the opposite side of reference angle C, because "C" is nowhere to be found in the sequence "ED".
The side CE = 45 is the adjacent side because "E" is found in "CE".
The tangent ratio is...
tan(angle) = opposite/adjacent
tan(C) = ED/CE
tan(C) = 28/45