Draw a diagram of the triangle to understand how the solution works.
Angle C is right angle, so c is the length of side opposite angle C, so it the hypotenuse, and so on.
if B=51, then a is the adjacent side to angle B (excluding hypotenuse).
therefore
a=c*cos(B)=23.5cos(51)=14.8
Note: question is confusing, because a is a length, but instructions require round off to nearest degree, so please check for typos.
