Genetics Question: Mapping Genes and Coefficients of Interference for trihybrid test-cross?

These are the steps:
1) Decide the parental types (biggest numbers) and double crossover types (smallest numbers)
Parental types: +bc and a++
dco types: +++ and abc

2) Determine the gene in the middle based on the parental and dco types.
The gene in the middle is a

3) Re-arrange the gene order:
+++ 2
bac 1
b++ 24
+ac 23
++c 39
ba+ 38
b+c 436
+a+ 437

4) Determine single crossover in region I (scoI) and in region II (scoII) based on the parental types:
scoI: ba+ and ++c
scoII: b++ and +ac

5) Calculate distance between b-a (region I) and a-c (region II)
Between b-a = (scoI + dco)/total x 100
= (38+39+2+1)/1000 x 100 = 8 mu
Between a-c = (scoII + dco)/total x 100
= (24+23+2+1)/1000 x 100 = 5 mu

6) The map is  b<----8---->a<---5-->c

7) Interference, I = 1 - c, where c is coefficient of coincidence
c = (observed dco)/(expected dco)
obs dco = 3/1000 = 0.003
exp dco = 0.08 x 0.05 = 0.004
c = 0.003/0.004 = 0.75
I = 1 - 0.75 = 0.25