The rate of change of temperature (-2.8°C/h) is multiplied by time (4h) to get the change in temperature (-11.2°C). That change is added to the initial temperature (20°C) to find the temperature after 4 hours.
Only equation A properly expresses this calculation.
In choice B, the rate of change is (wrongly) shown as +2.8°C/h. In the other choices, the combinations of units are nonsense. (What is a °C·h?)
The correct answer for part A is 5x² +7x -4. 5x³ -x² -8x -7 is the right answer for part B. Polynomials are always closed if under addition or subtraction. The answers of both parts A and B are polynomials. hope that helps let me know if it does
