Consider a simple macro model with a constant price level and demand$-$determined oufput. The equations of the model are: $C=150+0\mathrm{.}75Y,I=300,G=700,T=0,x=100,IM=0\mathrm{.}11Y.$ The marginal propensity to spend on national income, $z,$ is

A$.0\mathrm{.}833$

B$.0\mathrm{.}480$

C$.0\mathrm{.}668$

D$.0\mathrm{.}630$

E$.0\mathrm{.}640$