Suppose that the height (in centimeters) of a candle is a linear function of the amount of time (in hours) it has been burning. After 15 hours of burning, a candle has a height of 18.5 centimeters. After 31 hours of burning, its height is 13.7 centimeters. What is the height of the candle after 21 hours?

Astudent draws two parabolas on graph paper. both parabolas cross the x-axis at (–4, 0) and (6, 0). the y-intercept of the first parabola is (0, –12). the y-intercept of the second parabola is (0, –24). what is the positive difference between the a values for the two functions that describe the parabolas? write your answer as a decimal rounded to the nearest tenth