Let the numbers of trucks and cars be t and c. Then t = 1.5c.
c+45 - (t-12) = 17.
Simplifying the second equation, we get c + 45 - t - 12 = 17, or c + 33 - t = 17.
Substituting 1.5c for c, we get c + 33 - 1.5c = 17.
Solving this for c, we combine like terms: -0.5c = 17 - 33, or -0.5c = -16.
Then c = 32 and t = 1.5(32) = 48.
At the beginning there were 32 cars and 48 trucks in the lot. Answer: 32 cars, at the beginning.