Step-by-step explanation:
since I don't see a figure here, I have to use only the written information.
we need to remember :
tan(angle) = sin(angle) / cos(angle)
so, we have here
a/b = a/6 / cos(y) = a/(6×cos(y))
a×6×cos(y) = a×b
cos(y) = a×b / (a×6) = b/6
