Need help do not understand. Trig confused on what formula I should use?

In this triangle, you have
[tex]\sin35^\circ=\dfrac{12}x\implies x=\dfrac{12}{\sin35^\circ}\approx20.9[/tex]
(Think sine = opposite/hypotenuse. The leg opposite the labeled angle has length 12, and the hypotenuse is [tex]x[/tex].)