(a) Time period, $T = 2\pi\sqrt{\frac{1}{g}}$
$\frac{\mathrm{\Delta}T}{T} = \frac{1}{2}\ \frac{\mathrm{\Delta}l}{l} = \frac{1}{2}\alpha\mathrm{\Delta}\theta$
=$\frac{1}{2} \times 12 \times 10^{- 6}(40 - 20) = 12 \times 10^{- 5}$
$\mathrm{\Delta}T = T \times 12 \times 10^{- 5}$
= $24 \times 60 \times 60 \times 12 \times 10^{- 5}$
= 10.3 s ${day}^{- 1}$