A silica bulb of negligible expansivity holds 0.3kg of mercury at 00 C when fall. Some steel balls are introduced and remaining space is occupied at 00 C by 250gm of mercury. On heating the bulb and its contents to 1000 C, 5gm of mercury overflow. Find the linear expansivity of the steel.[γ=1.8*10- 6 / 0 C]​