A company manufactures $x$ units of one item and $y$ units of another. The total cost in dollars, $C$, of producing these two items is approximated by the function $$C = 4 x^2 + 2 xy + 3 y^2 + 900.$$

(a) If the production quota for the total number of items (both types combined) is 75, find the minimum production cost.
cost =

(b) Estimate the additional production cost or savings if the production quota is raised to 76 or lowered to 74.
production cost or savings =