Question

what is the formula of resistance?

Answer 1

Resitance of an object is the ratio of the potential difference across a conductor to the current flowing in a conductor.
R = V / I

Resistance of a conductor R = p L / A
p = resistivity of the conductor material = constant for that material
L = length of the conductor  used in the circuit
A area of cross section of the conductor  - used in the circuit

Answer 2

Resistance is the physical quantity that opposes the flow of current in a conductor.
R  = Potential Difference/Current flowing = V/I