Answer: 59.5 deg
Explanation: In this problem, we are giving 1.31 as n2 and 1.52 as n1. Using the formula of critical angle= arcsine(n2/n1) we get the equation critical angle=arcsine(1.31/1.52) from there, you divide 1.31 by 1.52, and get 0.862.
On your calculator you then should press 2nd and then the sine button to get sine^-1 (arcsine) and in the parenthesis after arcsine put in 0.862, the answer you get will be 59.5.