The lenght of the railroad at 40C is: ##30014.4m##

The formula that we need is the thermal dilatation formula:

##l_2=l_1(1+lambdaDeltaT)##

where

##l_1## is the initial lenght

##l_2## is the final lenght

##lambda## is the coefficient of

##DeltaT=T_2-T_1## is the amount of incresing (if it is positive) or decresing (if it is negative) of the temperature.

So in this case:

##l_1=30000m##

##l_2=Unknown##

##lambda=12xx10^-5C^-1## (steel)

##DeltaT=T_2-T_1=(40-0)C=40C##.

So:

##l_2=30000m(1+12xx10^-5C^-1xx40C)=30000m(1.00048)=300144m##.