The gulp method

The gulp method was used to determine the discharge of a mountain
stream. To determine the discharge, a 5 L tracer solution of 15,000 ppm
concentration was instantaneously injected in the stream. The
concentration C(t) was measured at the downstream sampling point,
and the discharge was determined as 3.85 L/s. During data
manipulation, the baseline concentration C0 data of the tracer was lost.
Based on the table below, determine C0.
Table Concentration C(t) measured at the sampling point.
t(s) C(t)
0     C0
2      457
4     3005
6      4270
8      2060
10    986
12    457
14    C0