URGENT PLEASE HELP If you answer this correctly ill answer some of your questions you have posted! (29pts)

How do you find the circumfrance of a circle?

The position of a moving particle is given by the position function: f(t)=-9t-t^2-0.2t^3+0.1t^4 a. at what time does the particle reverse direction? b. when is the displacement positive? (round one decimal place and answer in interval notation) c. when is the displacement negative? (round one decimal place and answer in interval notation) d. when is the particle’s acceleration positive? (round one decimal place and answer in interval notation) e. when is the particle’s acceleration negative? (round one decimal place and answer in interval notation)

Which value of m will create a system of parallel lines with no solution? y = mx - 6 8x - 4y = 12