Answer
137
Work Step by Step
Given $E=10,\sigma=59.50$, at a 95% confidence, the critical z-value is $z_{\alpha/2}=1.96$
and we have the equation $E=1.96\times\frac{59.5}{\sqrt n}=10$.
Thus, the sample size $n=(\frac{1.96\times59.5}{10})^2\approx137$ (round up to the next integer here)