A solenoid of 1.5 m in length and 4.0 cm in diameter possesses 100 turns per meter. A current of 5 amperes is flowing through it. The magnetic induction at the axis inside the solenoid is?

The magnetic field on the axis of a long solenoid is $B={\mu }_{0}ni$.

Where n is the no of turns per unit length and i is the current in the solenoid. 
Given:
n=100 turns per meter
i=5 A

$Absolute permeability \left({\mu }_{0 }\right) = 4\pi \times {10}^{-7 }H/m$

$B={\mu }_{0}ni$

$B=4\pi \times {10}^{-7}\times 100\times 5$

$B= 2\pi \times {10}^{-4} T$