plz.. solve it with some shortcut method

Q.- If three lines whose equations are y=m₁x+c₁ ,y=m₂x+c₂ & y=m₃x+c₃ are concurrent, then show that m₁(c₂-c₃) +m₂(c₃-c₁) +m₃(c₁-c₂)=0 .

Plz.. explain briefly how we can get the structure of Benzene( C6H6 )

 

Q. A person standing in a lift drops a coin from a certain height h.It takes time t  to reach the floor of the lift.If the lift is rising up with a uniform acceleration a, the time taken by the coin, dropped from the same height h, to reach the floor will be

 

(a) t  

 

(b) t sqrt.a/g

 

(c) t(1+a/g)^1/2       

 

(d) t(1-a/g)^1/2        

 

(plz.. dont forget to give explanation)