Explanation

(b)
$CaCO_{3}(s)\overset{\mathrm{\Delta}}{\rightarrow}CaO(g)(s) + CO_{2}(g) \uparrow K_{p} = 8 \times 10^{- 2}$
$K_{p} = \frac{p_{CaO(s)} \times p_{CO_{2}(g)}}{p_{CaCO_{3}(s)}}$
(Heterogenous equilibrium)
$K_{p} = p_{CO_{2}}$
$p_{CO_{2}} = 8 \times 10^{- 2}$
$CO_{2}(g) + C(s) \rightarrow 2CO(g),\ \ \ \ K_{p} = 2$
$K_{p} = \frac{p_{CO(g)}^{2}}{p_{CO_{2}} \times p_{C(s)}}$
(Heterogenous equilibrium)
$K_{p} = \frac{p_{CO}^{2}}{p_{CO_{2}}}$
$2 = \frac{p_{CO}^{2}}{8 \times 10^{- 2}}$
$p_{CO}^{2} = 2 \times 8 \times 10^{- 2}$
$p_{CO} = 0.4$ atm