Formula for the magnetic field inside a solenoid

[ashleyd]

A 29.8 mA current is carried by a uniformly wound air-core solenoid with 390 turns. the length of the coil is 13.1 cm, with a diameter of 20.8mm. The permeability of free space is 1.25664 X 10^(-6) N/A^2
compute the magnetic field inside the solenoid. answer in units of T

Relevant equations:
None

The attempt at a solution
no attempt, am stuck at what formula should be used

 

[cupid.callin]

you need formula ?

its B = μ_oni

 

[WatermelonPig]

integral(B dot dl) = Ithrough*mu0

Assume the solenoid is infinitely long. Well, if that is the case, then B inside the solenoid is constant. Anyways, If you draw two infinitely long rectangles, then you will get the formula posted above.