Answer:
The critical angle is

Step-by-step explanation:
From the question we are told that
The index of refraction of the glass in the fiber is

The index of refraction of the glass in the cladding is

The critical angle is mathematically evaluated as
![\theta_c = sin^(-1)[(n_c )/(n_f ) ]](https://img.qammunity.org/2021/formulas/physics/college/s9z2zp57tzjfveeh9ope4q54dl2zbjzwrn.png)
substituting values
