(a) For the end correction x, $\frac{l_{2} + x}{l_{1} + x} = \frac{3\lambda/4}{\lambda/4} = 3$ $\Longrightarrow \ \ \ \ \ \ \ \ \ x = \frac{l_{2} - 3l_{1}}{2}$ $= \frac{70.2 - 3 \times 22.7}{2} = 1.05cm$
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