We know that in equilibrium, $Y=C+I$ where, I is investment expenditure, given as 300 $Y$ is national income, given as 1500 and, $C=\overline{C}+cY$. here, $\overline{C}$ is autonomous consumption expenditure, given as $300, c$ is marginal propensity to consume. Thus, putting the values in the equation, we have $Y=\overline{C}+cY+I$. or, $1500\;=300+c\times1500+300$ or,$c\;=\;\frac{1500-600}{1500}=0.6.$ Thus, marginal propensity to consume is 0.6 .