We have,
$\mathit{Y}=\mathit{C}+\mathit{I}$
where,
$\mathit{I}$ is investment expenditure which is given as 100. $\mathit{Y}$ is income which is given as 1200 and, $\mathit{C}$ $=\overline{\mathrm{C}}+\mathit{c}\mathit{Y}$ here, $\stackrel{-}{\mathrm{C}}$ is autonomous consumption expenditure is marginal propensity to consumer, $\mathit{c}=1$ - marginal propensity to consume (mps) so, $\mathit{c}=1-0.20=0.80$. Thus, putting the values in the equation, $\mathit{Y}=\stackrel{-}{\mathit{C}}+\mathit{c}\mathit{Y}+\mathit{I}$ or, $1200=\overline{\mathit{C}}+$ $0.80\times 1200+100$ or, $\overline{\mathrm{C}}=1200-1060=140$. Thus, autonomous consumption expenditure is 140 .