\(\lambda\) is given by the relation,
\(E=\frac{\lambda}{2 \pi \varepsilon_{0} d} \Rightarrow \lambda=2 \pi \varepsilon_{0} d E\)
Where, \(d =2 \,cm =0.02 \,m , E =9 \times 10^{4} \,N / C\)
\(\varepsilon_{0}=\) Permittivity of free space and \(\frac{1}{4 \pi \varepsilon_{0}}=9 \times 10^{9} Nm ^{2} C ^{-2}\)
Therefore, \(\lambda=\frac{0.02 \times 9 \times 10^{4}}{2 \times 9 \times 10^{9}}=10\, \mu \,C / m\)
Therefore, the linear charge density is \(10\; \mu \,C / m\)