I would like to average N by Type for values of Inst

My data is set up as:

Type, Inst, N

A, A1, 4

A, A1, 13

A, A1, 13

A, A2, 4

A, A3, 5

B, B1, 4

B, b2, 10

So I would like to see a table (or bar chart) with A: 13, B:7. Any suggestions? If I put AVG(N) in rows and Type in columns I get A: 7.8, B:7

The problem is that Tableau is averaging all N per Type, but I want the numerator to be the total Nfor the Type while the denominator is the number of unique Inst within that Type