Simply change the words to equations and everything seems to always work out
First start by assigning meaningful variables. Let cars = c and let trucks = t.
The first sentence says "there were 6 more cars than 18 wheel trucks" So write c = t +6, agree?
Next, "There were 134 wheels in the parking lot". So what to do with this? Each car has 4 wheels and each truck has 18 wheels, right? So, in equation form this is:
4c + 18t = 134 total wheels.
Now just solve these two equations for c and t:
c = t +6
4c + 18t = 134
I recommend the"substitution" method for solving these two equations, but you can use any method that you like most.
Hope this helps