Answer:
5B; 7B; 1,024; see answer
Explanation:
5. 
We can see from the table that 
a1 = 5
a2= 5·2 = 10
a3= 5·2·2 = 5·2² = 20
a4 = 5·2·2·2 = 5·2³ = 40
...

7. 
Is given that the filter removes 90% of contaminated air 
after run 1 :
100% air 
90% contamination removed for 100% air
100% is 10%+10%+10%+10%+10%+10%+10%+10%+10%+10%
10% is still contaminated air 
after run 2:
10% air 
90% contamination removed for 10% air
10% is 1%+1%+1%+1%+1%+1%+1%+1%+1%+1%
1% is still contaminated air
after run 3:
1% air 
90% contamination removed for 1% air
1% is .1%+.1%+.1%+.1%+.1%+.1%+.1%+.1%+.1%+.1%
.1% is still contaminated air
11. 
Figure 1 = 1 piece 
Figure 2 = 4 pieces 
Figure 3 = 4² = 16 
...

12. 

-we know that the coefficients should be 1, 6, 15, 20, 15, 6, 1 
-we start with c to the lowest power 0 and d to the highest power 6 and end with d to the lowest power 0 and c to the highest power 6 

-we simplify to have the final answer:
