We first calculate d_{1} and d_{2}:
d_{1}=[\ln(S_{0}/E)+(R_{f}+½)×σ^{2}×t]/(σ×\sqrt{t})
=[\ln(80/70)+(.10+½×.30^{2})×.75]/(.30×\sqrt{.75})
=.9325
d_{2}=d_{1}-σ×\sqrt{t}
=.9325-.30×\sqrt{.75}
=.6727
From Table 23A.1, N(d_{1}) appears to be roughly .825, and N(d_{2}) is about .75.
Plugging these in, we determine that the option’s value is $17.12. Notice again that we used an annual t value of 9/12=.75 in this case.

Table 23A.1 Cumulative normal distribution