Problem with trend line fitting

If you want a fit that is linear in log-log space, then you need to do a log-log (power series) fit.

Select two cells, say A1 and B1, and array enter this: =LINEST(LN(C6:M6), LN(C4:M4))

That gives 0.8678 and -2.0914, meaning that the best-fit regression =EXP(-2.0914) * x ^ 0.8678. The 0.8678 is the exponent you see in your trendline, and =EXP(-2.0914) is 0.1235, the coefficient you see in your trendline.

If you want a linear fit, use =LINEST(C6:M6, C4:M4) to get the coefficients.