$4.$ Concrete sidewalks are always laid in sections, with gaps between each section. For

example, the drawing shows three identical $2\mathrm{.}4-$m sections, the outer two of which are

against immovable walls. The two identical gaps between the sections are provided so

that thermal expansion will not create the thermal stress that could lead to cracks. What

is the minimum gap width necessary to account for an increase in temperature of $32$

C$?-2\mathrm{.}4$ m Gap