$1.(8$ points$)$ Consider the following CMO structure backed by $8\%$ collateral:

Tranche Par Amount Notional Amount Coupon Rate

A $$300,000,0006\mathrm{.}50\%$

B $$250,000,0006\mathrm{.}75\%$

C $$200,000,0007\mathrm{.}25\%$

D $$250,000,0007\mathrm{.}75\%$

IO $?8\mathrm{.}00\%$

What is the notional amount of the IO tranche?