What is your "15 in length"? What does that correspond to? The length of the side opposite to the 30 degrees? What is b? The hypotenuse? What is a? The side adjacent to the 30 degrees?
so there's a right triangle
90 degrees in the bottom left
30 degrees bottom right
15 in length
unknown adjacent
unknown hypotenuse
so i did sin(30) = 15/b
15/sin(30)=30=b
and did tangent(30)=15/a
15 * tan(30)= 8.66=a
is this correct?