Answer: 67.5 seconds
Explanation:
The marble is traveling at a speed of 1/30 length units per 2.25 seconds.
Use direct proportion to find out the amount of time it would take to cover the whole length:
1/30 : 2.25 seconds
1 : x
1/30 x = 2.25 seconds
x = 2.25 ÷ 1/30
x = 2.25 * 30/1
x = 67.5 seconds
67.5 seconds is 1 mins and 7¹/₂ seconds.
