The derivative is -4t+3.
Work Step by Step
Whenever two or more functions are being added or subtracted, to find the derivative add or subtract the derivative of every single small function. Hence we have three small functions here. The derivative of $-2t^2$ is -4t, the derivative of +3t is 3 and finally the derivative of -6 is 0. Hence overall the derivative of f(x) is -4t+3.