Hi,
I am Nicola in the UK.
Stuck on a few questions.
Not looking to be spoon fed but some help would be great.
Here goes
A thin plus lens, made in glass of refractive index 1.50, has a focal length of +200mm and a concave surface radius of +125mm. What is the radius of the convex surface ?

If some one could talk me through it that would be great. :cheers: