The cost to produce n shirts is given as:

The cost function is a quadratic function with a positive leading coefficient, so the minimum value will be at the vertex of the function.
The vertex of a quadratic function can be calculated as:

a = coefficient of squared term = 0.4
b = coefficient of n term = -32
Using these values, we get:
This means, the cost will be minimized if 40 t shirts are produced. The minimum cost can be found by calculating C at n=40
So, the minimum cost will be:
C(40) = 0.4(40)² - 32(40) + 650
C(40) = 10
Therefore, the minimum cost to produce a t shirt will be $10