Help with inequality

Reflect the point (7,0) across the y-axis

Study results indicate that the mean length of time people spend on a bus in a city is between 21.2 min and 24.5 min what is the study margin of the error?

Which expression is equivalent to (5x^7+7x^8) − (4x^4−2x^8)? a. 9x^8 + 5x^7−4x^4 b. 3x^8 + 7x^7 c. 12x^8 − 2x^4 d. 5x^8 + 5x^7 + 4x^4