a. Fewer than 3

This is the only question i am stuck on. Please help!

Two ways to approach this. The hard way is to add together P(0 heads) + P(1 head) + P(2 heads). The easy way is to realize that P(less than 3 heads) = 1-P(3 heads); so if you can figure out P(3 heads) you can easily find P(less than 3 heads).