The first thing that you need to do is calculate the seed correction factor.  This is determined by setting up several bottles with large volumes of seed added to them.  The easiest way, in my opinion, is to use three bottles containing three, four, and five times the volume of seed that is added to your samples.  For example, if you add 3 mL of PolySeed to your BOD samples, you would add 9, 12, and 15 mL seed to your seed control bottles.  You incubate these bottles just the same as the samples and they have the same acceptance criteria.  Just for the sake of example I'll throw some numbers out there using the conditions I outlined.  

Seed control with 9 mL - initial DO 8.64  final DO 6.06 depletion= 2.58
Seed control with 12 mL - initial DO 8.59 final DO 5.41 depletion= 3.18
Seed control with 15 mL - initial DO 8.62 final DO 3.99 depletion= 4.63

You take each depletion amount and divide by the amount of seed added to the samples, in our example 3 mL.  This gives you (rounded to 2 significant digits) 0.86, 0.80, and 0.93 with an average value of 0.86.  This is your seed correction factor (SCF).
Now for the sample calculation.  Your sample had an initial DO of 8.67 and a final DO of 2.45.  The bottle contained 150 mL of sample.  Your calculation becomes [(Initial DO - Final DO)- SCF]*300/Sample Volume (mL) = [(8.67-2.45)-0.86]*300/150 = 10.72 mg/L.

thank you Mr David S.
your reply was useful for me too!!

I am not as familiar with respirometric BOD as I am with the normal 5 day, but I'll give this a shot. I presume you mixed the cream/water solution with domestic sewage to give it a bacteria population to work with. If so, that has become your seed source. The calculation is [oxygen uptake of sample-oxygen uptake of sewage*(0.5)]*(1000/actual volume of sample). In your case I guess you would substitute the actual volume of sample for the actual mass of the sample, 0.005 g in your case. You might try to get a density of the cream to convert it to volume, or presume a density near 1.0.