please help

Stock price=18

Strike price=20

Time to maturity=6 months

Volatility=30% per annum

RF Interest Rate=10%

Two dividends of 40 cents each, with one at 2 months and the other at 5 months

Based on this information, value the following:

1. American call using Black-Scholes-Morton model:

2. When should you exercise the above American call, and why?

3. The dividend is now 60 cents with everything else the same. When should you exercise the American call, and why? What is the value of the American call now?