How to find the focal length of a lens (Problem with a task)

[Sajo]

Homework Statement

Determine the optical power of a biconvex lens, with a radius of curvature of both spherical surfaces of 20 cm each, which is made of glass with a refractive index of 1.83 in water. The refractive index for water is 1.33

Relevant Equations

Optical power=1/focal length of lens

Hello. I need formulas for the focal length of a lens when I have refractive indices of two centers and two radii of curvature of spherical surfaces or one radius of curvature of spherical surfaces. I search the internet but can't find it.

 

[berkeman]

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Keywords are "Lensmaker Equation":

https://en.wikipedia.org/wiki/Lens#Lensmaker's_equation