852 - Math - Problem Solving

Question: An anti aircraft gun can fire four shots at a time. If the probabilities of the first, second, third and the last shot hitting the enemy aircraft are 0.7, 0.6, 0.5 and 0.4, what is the probability that four shots aimed at an enemy aircraft will bring the aircraft down?

1. 0.084
2. 0.916
3. 0.036
4. 0.964