S =20 the stock price

q = .5 = the probability the stock price will move upward

1 + rf = 1.1 = one plus the annual risk-free rate of interest

u = 1.2 = the multiplicative upward movement in the stock price

d = .67 = the multiplicative downward movement in the stock price

Solve for the current value of the call option using both a three-period and four-period binomial option pricing model