Mark and Trisha are traveling in the same direction and Mark is going 16 miles per hour. Trisha is going 12 miles per hour but started 8 miles before Mark. When will they meet up?
+36919 Their difference in spee is 16 - 12 = 4 mph
8 miles will take 8 / 4 = 2 hrs to catch up
+1224 Relative to Trisha, Mark is traveling at 4 miles per hour. Trisha has an 8 mile lead, so it will take Mark 2 hours to catch up.
