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Fred bought 3 cd’s for $16.50 is this multiplication division subtraction or addition

Find the slope and the y-intercept if there's one and the equation of the line given these two points( 3, 2) and( 3, -4)

The position of a moving particle is given by the position function: f(t)=-9t-t^2-0.2t^3+0.1t^4 0 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)