Mapping problem.. need help plz!

I was wondering if anyone knows how to solve/approach this problem. A group of people from my class have been working on it and we all come to different conclusions. Thanks in advance for your responses.

An E. coli F- strain has the following genotype: S-U-R-I-E-C-. Three different Hfr strains, all carrying S+U+R+I+E+ and C+ markers and all having lambda phages integrated at the same specific site in their chromosomes are mated with the F strain in separate matings. The interrupted-mating results are given below. The numbers indicate time (in minutes) when different donor markers appeared in F- cells after conjugation began. Assume that the E. coli map consists of 100 minutes and gene C is mapped at 80 minutes.

Markers Hfr 1 Hfr 2 Hfr 3

R 10 20 –

I 40 – 5

U 25 5 –

E – 60 –

C – 45 –

S 55 – 20

The positions of Hfr 2, the gene C, and the polarity of Hfr 2 are given in the accompanying map. (please see picture attachment)