working out a substrate concentration
 

Hi,
I have to do a pratical report and need to calculate the substrate concentration of G-1-P but have forgotten how to. Stock solution is 4mM. 6 test tubes with different volumes of 4mM G-1-P (volumes were 0.1ml, 0.2ml, 0.4ml, 0.8ml, 1.6ml, 2.4ml ) giving a total of 4ml in tube once added to other substances. Would be grateful for any help please!
Many thanks in advance
Mel