How much do you earn for a delivery?

Calculation of Revenues:

There is a series of four calculations that are run on each commodity on each delivery. They must be done in the order listed in this chart. The total revenue for the run is determined by adding the results of the calculations below for each commodity. To that will be addad any station-specific modifiers such as restraunt/hotel income for passenger deliveries.

Variables:
DIST = # squares between stations (* .5 if E. USA or England)
DISTB and DISTC = Interim variables in formulas SPEED = Mph/2.5 (i.e. 20mph = speed of 8) CLASS = 0 for Ma, 1 for Passenger, 2 for Fast Freight, 3 for Slow Freight and 4 for Bulk Freight)
DIFF = Difficulty level (0 for investor ... 3 for Tycoon)
REVENUEA = Interim variable in formula
FIRST YEAR = The first year of the scenario
REVENUE = Revenue for cargo

Calculation #1: Effect of Distance
DISTB = DIST*(5 - CLASS) + (40*(CLASS+1))

Calculation #2: Effect of Speed
DISTC = (DISTB/8)*(SPEED + (2*CLASS^2) / (((YEAR-1790)/10) + (2*CLASS^2))

Calculation #3: Effect of Year
REVENUEA = TONS*2*DISTC / (YEAR - (1170 + (FIRST YEAR/3)))

Calculation #4: Effect of Difficulty Level
REVENUE = REVENUEA * (7 - DIFF) / 6

I've found these formulas here and here,both quoting "The Official Guide to Sid Meier's Railroad Tycoon" as their source.