[Closed] Calling mathematicians/geophysicists (Snell's Law content)

I'm doing a geophysics module at the moment and not having done any trig-related maths for decades, I'm struggling with what are some fairly basic stuff.

I can derive results from equations, but the difficulty comes when rearranging equations to derive a different function.

As an example, the basic equation is: sin i/sin r = v1/v2

I'm familiar with the basics of trig, i.e. SOCAHTOA, but i's mainly the rearranging thing.

You've also got t = 2h/(V1 cosiC) + (x - 2h tan iC)/V2
(time taken for head wave)

I understand the principles of Snells Law, and the whole thing with refraction and relfection. However, it's the maths I'm having a bit of a blank with at the moment.

Does anyone have any Snell's Law for dummies tips or guides?