Help with Diffusion Homework: Find Concentration 300mm from Closed End

[Kimko]

Homework Statement

We have a tube filled with water where there is a plug of substance at one closed end. Diffusion constant of this substance is known and its concentration at t=0 is given as:
Co(x)= 10mg/ml if x<= 100mm
Co(x)= 0mg/ml if x> 100mm
Distribution of particles from the plug in 1-D is given as:

C(x,t)=1/(4piDt)^(1/2) * int{ Co(x') e^[-(x-x')^2/(4Dt)] dx'}

Write an expression for the concentration of the substance (in integral form) as seen 300mm from the closed end.

The Attempt at a Solution

I assume that x=100mm and x'=300mm
I really don't know what to do next, need help.

 

[BigJDubs]

C(x,t)=1/(4piDt)^(1/2) * int{ Co(x') e^[-(x-x')^2/(4Dt)] dx'}C(300mm,t)=1/(4piDt)^(1/2) * int{ Co(300mm) e^[-(100mm-300mm)^2/(4Dt)] dx'}