We know that the rail expands in both the directions, so the gap between two rails will be filled by the expansion of half length of each rail. For this we take the expansion of one rail in one direction to fill the gap.
Here,`l= 60 m , l = 3.60 cm = 3.6 xx 10^(-2) m`,
`theta_(1) = 10^(@)C , theta_(2) = ? , alpha = 11 xx 10^(-6)` .^@)C^(-1)`
`alpha = (Delta l)/(l(theta_(2)-theta_(1))) or theta_(2) - theta_(1) = ( l)/(l alpha)`
or `theta_(2) = theta_(1) + (Delta l)/(l alpha) = 10 + (3.60 xx 10^(-2))/(60 xx 11 xx 10^(-6))`
`= 10 + 54.54 = 64.54 .^(@)C`