Answer:
11) 
Divide both sides by 2:


12)
(
if you wanted the exact value.
13) 
Switch sides:

Rearrange:


14) 



15) 




16) 
Multiply both sides by 4:


17) 
if you wanted the exact value.
18) 
if you wanted the exact value.
Bonus Question:
Terrorist attacks took place against the United States in September 11 2001.
This is named "September 11 attacks" and you can search more about it online.
Answer:
20%
Step-by-step explanation:
4 / 20 = 0.2 = 20%
Hope this helps :)
Step-by-step explanation:
a) 4x + 8 - 2x + 7
= 2x +15
b) 2n × 5 × 2a
= 10n × 2a
= 20an