Please determine the accurate answer of the following Problem

Problem-A series of 4 layers has the following structure and velocities. Layer 1 has its upper surface at the ground surface. It has a p-wave seismic velocity of 2.5 km/s. Below it are three more layers with p-wave velocities as follows: V2=3.5 km/s, V3=4.5 km/s, V4=6.0 km/s. At the interface between layers 3 and 4, the ray travels parallel to the interface after refraction. This is called the critical angle and it occurs when the angle of refraction (i²) is 90° and sin(i²)=1.

Part 1- What are the incident angles in layers 3, 2, and 1?

I need assist to compute the incident angles in layers first and second