i have to use either sin, cosine, or tangent?
You need to learn by heart:
$\displaystyle \sin(\theta)$ is "opposite leg divided by hypotenuse".
$\displaystyle \cos(\theta)$ is "near leg divided by hypotenuse".
$\displaystyle \tan(\theta)$ is "opposite leg divided by near leg".
In your diagram the hypotenuse has length 15 and the side opposite the 53 degree angle has length x.