Ideal Mechanical Advantage of this bicycle?

[Rionic]

A bicycle wheel has a diameter of 73cm and is driven by a chain on a gear of 8.5cm diameter

What is the ideal mechanical advantage?

I know that IMA=de/dr
But I'm not sure which one is de and which one is dr.

 

[billy_joule]

I'm not sure where you got that equation from but the normal form is:

MA = Force in / Force out

https://en.wikipedia.org/wiki/Mechanical_advantage

Can you find the MA now? If not, can you identify the force in and force out?

 

[Rionic]

I'm not sure where you got that equation from but the normal form is:

MA = Force in / Force out

https://en.wikipedia.org/wiki/Mechanical_advantage

Can you find the MA now? If not, can you identify the force in and force out?

Force input= 8.5 and force output=73?

 

[billy_joule]

Those are distances, in cm, not forces.
But your idea is right and will give the right answer.
One way is to consider it as a 3rd class lever, the axle is the fulcrum, the effort is applied via the chain and the load is at the tyre contact point.