Seek inclusion of primary factors. Helpful in using boat ramps to launch and remove a boat from water, to determine number of people needed, safety, need for winch, need for motor assist, need for wheel stops, etc. Helpful in learning the effort saved in employing two wheels to any load. Assume bearings, friction, wheel flex, and slope surface are not impacts. Include variance for wheel size, changes in slope degree or % and load. Wheels at or near the balance point of load. Looking for a simple formula as opposed to inclusive of all or lesser factors.
Define equation symbols, increments and constants for use as: F = force in (what) pounds, etc. Also is theta the degree of rise or other? Give an example and result for shadow effort. Indicate omitted factors not included. Why is there no wheel diameter included?

A ferry carries 25 passengers. The weight of each passenger has a normal distribution with mean 168 lbs and variance 361 lb squared. Safety regulations state that, for this particular ferry, the total weight of passengers on the boat should not exceed 4250 lbs more than 5 percent of the time. What is the probability that the total weight of passengers on the ferry will exceed 4250 lbs?