Answer:
Thus, the payback time for cavity wall insulation is 7.5 years
 
        
             
        
        
        
Answer: 
Explanation:
Given
Current in the first wire 
Current in the second wire 
wires are 
 apart
Force per unit length between the current-carrying wires is 

Force exerted  by the wires is the same
Put the values

This force will be repulsive in nature as the current is flowing opposite
 
        
             
        
        
        
Answer:
noble gases are basically a group of gases that are similar in their chemical compounds, theres six of them : helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and the radioactive radon (Rn). 
~batmans wife dun dun dun.....