A closely wounded circular coil of radius 5cm produces a magnetic...

Given here, $N = 100$, $R = 5cm$ and $B = 37 . 68 \times {10}^{- 4}T$

Magnetic field at the centre of circular coil is given by ${B}_{centre} = \dfrac{N{\mu}_{0}l}{2R}$.

Putting the values,

$37 . 68 \times {10}^{- 4} = \dfrac{100 \times 4\pi \times {10}^{- 7} \times I}{2 \times 5 \times {10}^{- 2}}$

Current through coil is $I = 3A$.