For beginners to Mma:
In[1]:= data = {{5, 99}, {6, 164}, {9, 423}, {10, 647}}
Out[1]= {{5, 99}, {6, 164}, {9, 423}, {10, 647}}
In[2]:= FindFit[data, k E^(a t), {k, a}, t]
Out[2]= {k -> 16.3433, a -> 0.366346}
In[3]:= f[t_] := 17.395 E^(0.3597 t)
In[43]:= Plot[f[x], {x, 1, 22}]
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