Let $C(x)=15x1300$ denote the total cost $($in dollars$)$ of manufacturing $x$ units of a certain commodity per day.

a$)$ What is the total cost if the production is set at $30$ units per day?

b$)$ What is the marginal cost?

c$)$ Use b$)$ to determine the additional cost of raising the daily production level from $30$ to $31$ units.

a$)$ The total cost of producing $30$ units per day is $