What is the formula in getting the average speed?

Express the distance covered per hour.
Add the distances and divide by the number of hours.

If a boat covers 68 miles in 29.47 minutes.
Do I multiply 68 by 60 (for minutes), which equals 4080. Then divide that by 29.47 for minutes taken.
Which equals, 138.4 mph for average speed.

jobe, use:

Speed = \frac{Distance}{Time}

and that's all.

If you use time in minutes, then you have \frac{miles}{min}

And if you use hours, then you have \frac{miles}{hour}