(b) Slope of $V_{0} - v$ curve $= \frac{h}{e}$ $\Rightarrow h = Slope\ \times e = 1.6 \times 10^{- 19} \times 4.12 \times 10^{- 15}$ $= 6.6 \times 10^{- 34}J$-$s$
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