Magnetic Field inside a Solenoid (Please explain this answer to me)

[Strawberry]

Homework Statement

Q5. A solenoid is 3.0 cm long and has a radius of 0.50 cm. It is wrapped with 500 turns of wire carrying a current of 2.0 A. T

Homework Equations

Magnetic field of an ideal solenoid = permeability constant (1.257E-6) * current * number of turns

The Attempt at a Solution

The given answer is: 4.2 x 10-2 T

I don't understand how to get this answer. From what my book says, the magnetic field is independent of cross-sectional area and only deals with semi-infinite solenoids. Please help!

 

[Strawberry]

err nvm, I figured it out. I was seriously staring at this thing for two hours and then finally figure it out after I post it ><