if a steel flagpole get 5.1 mm taller when temperature increase by 5.0 degree celsius approximately how tall is the flagpole?

Answer 1

Look up the coefficient of thermal expansion of steel. Call it a.

a*L*(deltaT) = 0.0051 meters

Solve for L.
L = 0.0051/(a*deltaT)
"deltaT" = 5 C