How do I calculate focal length from L and U measurements?

[math4me]

I am trying to find F, i have L = 60cm and U = 31cm, how would i calculate f (focal length)?

and also how would i find the uncertainties?

thank you very much

 

[Kurdt]

Not sure about the uncertainties but I assume U and L are object and image distances so the formula you need is

$$\frac{1}{L} + \frac{1}{U} = \frac{1}{F}$$