Answer:
N = 3032 turns
Explanation:
The magnetic field produced by a solenoid is described by
B = μ₀ n I
Where is the permittivity in a vacuum with a value of 4π 10⁻⁷ N /A², n is the turn density and I the current
Let's apply this equation to the problem, the turn density is the number of turns per unit length, in this case it is the same magnet length
L = 8 cm = 0.08 m
Let's calculate
B = μ₀ N/L I
N = B L / μ₀ I
N = 0.10 0.08 / (4π 10⁻⁷ 2.1)
N = 3,032 103 turns