Answer:
B = 0.025T
Step-by-step explanation:
In order to calculate the strength of the magnetic field at the center of the solenoid, you use the following formula:
(1)
μ: magnetic permeability of vacuum = 4π*10^-7 T/A
N: turns of the solenoid = 500
i: current = 4.0A
L: length of the solenoid = 0.10m
You replace the values of the parameters in the equation (1):

The strength of the magnetic field at the center of the solenoid = 0.025T