Calculate a mean on condtions in a dataframe with dyplr

My table looks like this:

    Tissue  Dry Amount   Analyte            Area
1   Liver   A   a   3-Phosphoglyceric Acid  66351918.4
2   Liver   B   a   3-Phosphoglyceric Acid  119013081.6
3   Liver   A   b   3-Phosphoglyceric Acid  195732464.0
4   Liver   B   b   3-Phosphoglyceric Acid  247443210.8
5   Liver   A   c   3-Phosphoglyceric Acid  456447252.7
6   Liver   B   c   3-Phosphoglyceric Acid  494555301.1

I would like to get the mean of the two values for the same Tissue Amount and Analyte by ignoring the DRY variable.

I always end up having one value of the two and not the mean.

Summary - shape.data %%
+   group_by(Amount,Tissue,Analyte ) %%
+   summarise(Area_mean = mean(Area))

How can I do this calculation?