Calculate the linear expansivity of a material of length 120m that assumes a new length of 12.05m when heated through a temperature of 90°C

Answer 1

Surely you mean the length was 12.0m. If so, then
12.05 = 12.0(1 + 90α)
1 + 90α = 1.004167
α = 0.004167/90 = 0.0000463