Answer
The number of elements in set A but not in set C = 6.
Work Step by Step
From the given Venn diagram,
the regions I, II belongs to set A but not set C.
It's given from the Venn diagram that:
The number of elements belongs to region I = 5
The number of elements belongs to region II = 1
Therefor The number of elements in set A but not in set C = 5 + 1 = 6.