Resposta :
B = μ0 . i / 2R
4,5.10^-7 = 4π.10^-7 . i / 2.4
4,5.10^-7 = 4π.10^-7 . i / 8
4,5.10^-7 . 8 = 4π.10^-7 . i
36.10^-7 = 4π.10^-7 . i
36.10^-7 / 4π.10^-7 = i
36.10^-7 / 4.3.10^-7 = i
36.10^-7 / 12.10^-7 = i
3.10^-7-(-7) = i
3 = i
i = 3 A
alternativa b) ✓