physics homework- thermal expansion....help!!!?

[Chel]

If a concrete highway is built in slabs of 12m long, how wide should the expansioncracks be (at 15 degrees celsius) between the slabs to prevent bucklingif the range of temperature is -30 to +50 degrees celsius?

And also at what temp will the fahrenheit and centigrade scales yeild the same numerical value?

any help would be greatly appreciated!!!! I am not so good at physics.
for the first question the coefficients of expansion at 20 degrees celsius is 12 times 10^-6