Answer
$E = 6.8\times 10^9~N/m^2$
Work Step by Step
In part (a), we found that the strain is $~~1.9\times 10^{-3}$
In part (b), we found that the stress is $~~1.3\times 10^7~N/m^2$
We can find Young's modulus $E$:
$E = \frac{stress}{strain}$
$E = \frac{1.3\times 10^7~N/m^2}{1.9\times 10^{-3}}$
$E = 6.8\times 10^9~N/m^2$
