ATC=30/Q+(3+Q)-----(DIVIDED BY Q) IF YOU MAKE Q THE COMMON DENOMINATOR THEN

ATC=(30+3Q+Q^2)/Q.

4D. MARGINAL COST IS THE CHANGE IN TOTAL COST (OR VARIABLE COST) WITH RESPECT TO (WRT) A CHANGE IN QUANTITY. SAME AS DIFFERENTIATING THE TC FUNCTION OR VARIABLE COST FUNCTION WRT TO Q.

NOW VC FUNCTION IS ....10Q-6(Q^2)+Q^3

IF WE DIFFERENTIATE WRT TO Q WE HAVE 10-12Q+3Q^2

NOTE THAT IF WE USED THE THE TC FUNCTION IT WOULD BE THE SAME BECAUSE 1000 IS A CONSTANT SO IF IT IS DIFFERENTIATED IT IS 0.

NOW WITH Q=10 WE SUBSTITUTE TO GET 10-120+300=$190.

PS: REMEMBER TO USE YOUR UNITS.

EVERYTHING ELSE IS GREAT...GOOD JOB. HOPE I HELPED.