Fitting data with a negative exponential
 

I have a number of data points that appear to fit a negative
exponential model. When I graph the data in Excel that is how it
looks. However, the trends that Excel allows do not appear to fit
negative functions. Can someone tell me how to modify the trend
fitting capability of Excel to handle this data.

Please post detailed steps. I am looking a cancer data that I need to
model and display.

Thanks,

oldman