[b]2. sinΘc = n2/n1
[b]3. I did this equation with air as n2 and glass as n1 and then got Θc=42.5°. After that I subtracted that from the normal (90°) and got 47.5°. Is this the right way to approach this? Just for the record this is for AP Physics B so no calculus should be used. Thank you!