The function is .

(a).

Graph :

Graph the function :

(b).

Graph :

Graph the function :

Observe the graph:

A downward slope but also where the slope is getting less steep with each additional lawn mower manufactures.

Find the values of when .

When , .

.

When ,

.

When ,

.

When ,

.

When ,

.

Observe the above values, 

Manufacturing mowers gives an average cost of .

Manufacturing mowers gives an average cost of .

Manufacturing mowers gives an average cost of .

The minimum point is .

The number of  riding lawn mowers to produce in order to minimize average cost is .

(c).

The minimum average cost is when produce mowers.

The cost is /mower.

(a).

Graph of the is

(b). riding lawn mowers per hour.

(c). /mower.