First we need to find the upper angle of triangle ABC to do this we can use the inverse tangent function (arctan) of the side opposite the angle divided by the side adjacent to the angle.
arctan (53/37) = 55.0806, this can be used to find the upper angle of triangle BCD by subtracting 90 by the angle we just found: 55.0806.
90 - 55.0806 = 34.9194
This angle (34.9194) is the upper angle of the smaller triangle and can be used along with the side 37 (BC) and the tangent function to find CD.
tan(34.9194)= (CD)/37, multiply both sides by 37 to isolate CD and plug it in your calculator.
37 x tan(34.9194) = CD = 25.8302
Rounding shows us that A, 26 is correct.