The most simple answer is to put the $30k towards the highest interest debt. I'll guess your mortgage rate will be ~4%. So, if you have student loans greater than 4%, pay those off first. If you pay all student loans off greater than 4% and have some left over, add it to down payment of the house.
Either way, if you're not upside down on the car, get rid of it. Maybe even use $6k cash to buy a Honda/Toyota used.
Quick example:
Current Car = $27,000
Used Honda/Toyota = $6,000
$21k difference over 4 years ($429/mo).
Invest that $429/mo to the tune of $24.5k at the end of four years, if the market averages 7%.
At the end of 4 years you could have the car you have now, and $0. Or a used Civic & $24.5k.
Of course, I don't know how upside down you are, so this may not work out so well. Cars are awful.