i have a word problem and no clue at all how to attempt it, so once again i turn to you folks for help

A bicycle has two sets of gears, one at the pedals and one at the rear wheel. A typical 10-speed bicycle has two gears on the chain wheel and five gears on the rear wheel. The spead at which a bicycle travels depends on three independent factors:

-The first is the speed at which the cyclist pedals to turn the front gear (measured in RPM)

-The second is the gear ratio from front wheel to rear wheel (a ratio between number of teeth on the front gear compared to the number of teeth on the rear gear.)

-The third is the size of the rear wheel (measured as the diameter of the wheel.)

i need to come up w/ a formula that models this but the closest i've come is

where t is the number of teeth