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)
>>>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.)
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.