Question

The S−S bond distances in S8 are 204 pm and the F−F bond distance in F2 is 143 pm. Use these values to estimate the S−F bond distance in S2F2.

Answer 1

the bond distance in the S-S is the distance between the nucleus of the two atoms, if you divide by 2 you will get the radius of a single S atom.
The same logic can be used with the F-F bond.
To calculate the distance between S-F you just have to add the two radius distances. Assuming that all are single bonds