It should not be that difficult. It is only a substitution, or plugging in, problem. Nothing to analyze really. That is if you know the formula and constants to use.

The question is about linear thermal expansion of a length of steel.

In Physics we learned for this case that

"the change in length is proportinal to the change in temperature"

delta L ----> L*(delta T)

delta L = k*[L*(delta T)] -------(i)

where

>>>delta L is (change in length) = (final length minus initial length)

Or, (final length) = (initial length) +(delta L)

>>>k = constant of proportionality = average coefficient of linear expansion.

For steel, k = 11*[10^(-6)] per degree Centigrade

>>>L = initial length

>>>delta T = change in temperature = (final temp. minus initial temp.)

Given:

L = 11.5 m

delta T = (1221 -22) = 1099 deg Celsius

So, substituting all those into (i),

delta L = [11*10^(-6)]*[11.5 * 1099] = 0.139 m

Therefore, that piece of steel is

11.5 + 0.139 = 11.639 m long

when its temperature is 1221 degrees Celsius.