Question 891952
There are 64 possible outcomes. 
0 heads - 1
1 head - 6
2 heads - 15
3 heads - 20
4 heads - 15
5 heads - 6
6 heads - 1
.
.
.
a) {{{P(3H)=20/64=5/16}}}
b) {{{P=(1+6+15+20)/64=42/64=21/32}}}
c) Of the 64, only half of them start with a head on the first toss. 
Of those 32, only half of them end with a head on the last toss.
{{{P=16/64=1/4}}}