that the risk$-$free rate for this time step is $R.$

You may use the notation used in the text to show that for any given number $a,$ if

$N=({}_V-a)\frac{V(0)e^{rt}}{f(0,T)},$

then ${}_{\text{w}\text{i}\text{d}\text{e}\text{t}\text{i}\text{l}\text{d}\text{e}(V)}=a.$