A1=10 ai = ai-1 * 9/10 Find the sum of the first 75 terms in the sequence

Having a hard time understanding this question (see attachment).

Which best describes the function on the graph? direct variation; k = −2 direct variation; k = -1/2 inverse variation; k = −2 inverse variation; k = -1/2

Find the rate of change for the situation.you run 7 miles in one hour and 21 miles in three hours.