The yield to maturity $($YTM$)$ on $1-$year zero$-$coupon bonds is $6\%$ and the YTM on $2-$year zeros is $7\%.$ The yield to maturity on $2-$year$-$maturity coupon bonds with coupon rates of $13\%($paid annually$)$ is $6\mathrm{.}4\%.$

a$.$ What arbitrage opportunity is available for an investment banking firm?

b$.$ What is the profit on the activity? $($Do not round intermediate calculations. Round your answer to $2$ decimal places.$)$