1 Liter = 1000 mL, you know the concentration per liter, therefore how much toluene (in moles) is present in 1 mL?
Keep going until you reach solution no 8.
You know the concentration in moles of solution 8 therefore you know the number of molecules.
Or you can start by working out how many molecules are in 1 mL of solution 1 and so on until you reach solution 8, therefore you know the concentration.
There is probably a mathematical formula for this but I don't know it!