I used t but I guess you could use any variable you want to represent time. The equation is the rate of the car times the time it took to reach the destination set equal to the rate of the bike times the time it took to reach the same destination. Because the destination is the same, d is the same for both. The transitive property tells us that if the distances are the same, then the rates and times are the same as well, so we can set them equal to each other. That's what all that means. Don't you just love these motion problems?! lol
