Please help me with this question: calculate the speed of light inside the water using this measurement of n from the slope

Water Angle of incidence Angle of refraction 10 5 6 20 140 30 22 0 40 29 0 50 BS - 60 420 70 490 80 550 . Slope of sin (01) vs. sin(02) = nw :...2..4.u.V.. %% error of nw compared to the accepted value 1.33 = .. 6.!. Critical angle: 0c = .......... .; nw = 1/sin ( 0 ) = ..1 33) % error of nw compared to the accepted value 1.33 = 0-075 % sind Z 1.33 Oc ~ 487