First and Second Order Derivative. Please help?

Hey Guys, I'm having some serious trouble with a profit function, and hoping someone can help soon!

TT= (aQ-bQ^2)-(t(aQ-bQ^2) + cQ).

which could then be this:(I think)

TT= (aQ-bQ^2)-(taQ-tbQ^2) + cQ): But, can I skip this part and just find the First-Order?

I need to find the First and Second Order derivitives, but the extra variable (t) is the one I'm having problems with. In this function (t) represents taxes, (just FYI).

First thing I tried was this: First-Order = (a-2bQ) - (at-2bQt+c)

Do I also need to take the partial derivative of (t)?

Second-Order = is also trippin me up.

If anyone can help I would be very thankful. (Wondering)