Use pemdas 5^2 + 3^2 x (7 - 3) use 3 steps

Hi my sisters and brothers can tell me the answer because i don’t understand the question

Which equation results from adding the equations in this system? x+6y=9 and -x+2y=-15

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)