$(60$ points$)$ Consider a money demand function given by

mD

t $=\backslash$phi yt

$($

$1+$ Rt

Rt

$)$

$(1)$

and the central bank sets the money supply exogenously, such that

mS

t $=$ mD

t $(2)$

$($a$)(10$ points$)$ Suppose income is yt $=100,$ nominal interest rates are Rt $=0\mathrm{.}10,$ and

the $$usefulness of money$\backslash$phi $=0\mathrm{.}99.$ What is the money supply?