The resonance conitionis given by  :h f= g mB B where 

h =Planck's constant =6.62 10-34 J.s

f = frequency ( Hz)

mB : Bohr magneton = 9,2740154 10-24J/T

B: Magnetci field(induction) in Tesla

g=Lande factor

Ex: 

Apparatus with f =9.63 GHz =9.63 109 Hz

B (at resonance) =  0.3433 T

g =h f/ mB B = (6.62 10-34*9.63 109)/(9,2740154 10-24*0.3433)= 2.00443

N.B :  actually "g" is a tensor, it depends strongly on the cristallographic geometry of compounds  and the other magnetic couplings as spin-orbite, exchange, ....

Consult the following text:

W Low, Paramagnetic Resonance in Solids, in Solid State Physics, Supplement 2, edited by F Seitz and D Turnbull (Academic Press, New York, 1960).

See in particular Eq. (2.1a), p. 4, herein.

I attach blow also two relevant pages made available by University of Californian, Davis.

https://chem.libretexts.org/Core/Physical_and_Theoretical_Chemistry/Spectroscopy/Magnetic_Resonance_Spectroscopies/Electron_Paramagnetic_Resonance/EPR%3A_Theory

https://chem.libretexts.org/Core/Physical_and_Theoretical_Chemistry/Spectroscopy/Magnetic_Resonance_Spectroscopies/Electron_Paramagnetic_Resonance/EPR%3A_Interpretation

The resonance conitionis given by  :h f= g mB B where 

h =Planck's constant =6.62 10-34 J.s

f = frequency ( Hz)

mB : Bohr magneton = 9,2740154 10-24J/T

B: Magnetci field(induction) in Tesla

g=Lande factor

Ex: 

Apparatus with f =9.63 GHz =9.63 109 Hz

B (at resonance) =  0.3433 T

g =h f/ mB B = (6.62 10-34*9.63 109)/(9,2740154 10-24*0.3433)= 2.00443

N.B :  actually "g" is a tensor, it depends strongly on the cristallographic geometry of compounds  and the other magnetic couplings as spin-orbite, exchange, ....

thank you @ Mohamed El Hafidi

Thanks alot sir

Calculate by the expression;

hν = g µo Bo

Where, h = Planck’s Constant = 6.626 x 10 -34 J S

ν = Microwave frequency = 9.8623 GHz x 1000 = 9862.3 MHz (must know)

µo = Bohr Magneton = 9.27 x 10 -24 J/T = 9.27 x 10 -27 J/ mT

Bo = Magnetic field strength = 3400 G (lets say)= 3400 X10 -4 T = 3400X10 -7 mT

g = hν/µoBo, Bo = 6.626 x 10 -34 JS x 9862.3 MHz / 9.27 x 10 -27 J/ mT X 3400X10 -7 mT

g = 2.07183