15. The current price of a stock is 100. Suppose that the logarithm of the price of the stock changes according to a Brownian motion with drift coefficient ì = 2 and variance parameter ó2 = 1. Give the Black-Scholes cost of an option to buy the stock at time 10 for a cost of

(a) 100 per unit.

(b) 120 per unit.

(c) 80 per unit.

Assume that the continuously compounded interest rate is 5 percent.

A stochastic process [Y(t)> t > 0} is said to be a Martingale process if, for s < t9 E[Y(t)\Y(u)9 0 < u < s] = Y(s)