so hmm notice the picture below
thus [tex]\bf \cfrac{y}{tan(64^o)}=\cfrac{y}{tan(46^o)}-100\implies
\cfrac{y}{tan(64^o)}-\cfrac{y}{tan(46^o)}=-100
\\\\\\
y\left[ \cfrac{1}{tan(64^o)}-\cfrac{1}{tan(46^o)} \right]=-100\implies y=\cfrac{-100}{\frac{1}{tan(64^o)}-\frac{1}{tan(46^o)}}[/tex]
make sure your calculator is in Degree mode, since the angles are in degrees