Remember what Snell's law says:

sin(x1)/sin(x2) = v1/v2 = L1/L2 = n2/n1

where: - x1 is the angle between the normal and the ray of light when entering the new material

- x2 is the angle between the normal and the ray of light when after entering the new material

- v1 is the speed of light in material 1

- v2 is the speed of light in material 2

- L1 is the wavelength of light in material 1

- L2 is the wavelength of light in material 2

- n1 is the refractive index of material 1

- n2 is the refractive index of material 2

i suppose you're going from air to glass. the refractive index of air is 1.0008, let's just use 1

you only need

sin(x1)/sin(x2) = n2/n1

for your question. so fill in everything except what you want to find.

you want an angle of 25 degrees after entering the new material, so

sin(x1) = (n2/n1) * sin(x2)

= 1.54/1 * sin(25)

= 0.650832123

=> x1 = arcsin(0.650832123) = 40.6 degrees ......this is the angle you must enter the new medium at