Stuck with some basic maths probabilty.....

Heres my question guys:
[b]a component is made in 3 stages. the first stage involves building from one of four machines A,B,C and D all with equal probabilites. Second stage is trimmed using one machine either E,F or G, and finally polished using either machine H or J and it is twice as likely to be the former as H works faster[b]

Determine the porbabilty of:
1. a component is polished on machine H
is it 2:1?

2. it is trimmed on either machine F or G
2/3 or 66%

[b]3. a component is formed on either machine A or B, trimmed on F and polished on H]/b]
i have no idea

4. it is formed on machine A and polished on J

5. formed on machine B and polished on machine H

6. formed on machine A and trimmed on F
A = 1/4 or 0.25, F = 1/3 or 0.3
0.25 x 0.3 = 0.075
0.25 + 0.3 - 0.075 = 0.475 or 47.5%
is that right?

any help on this guys would be a big help, show working out too?