Answer
$0.19nJ$
Work Step by Step
We can find the required work done as follows:
$W=K.E_f-K.E_i$
We plug in the known values to obtain:
$W=(\frac{m_{\circ}c^2}{\sqrt{1-v^2/c^2}}-m_{\circ}c^2)-0$
$\implies W=m_{\circ}c^2(\frac{1}{\sqrt{1-v^2/c^2}}-1)$
We plug in the known values to obtain:
$W=1.673\times 10^{-27}(3.00\times 10^8)(\frac{1}{\sqrt{1-(0.90)^2}}-1)$
$W=0.19nJ$
