29. In the parking lot, there were passenger cars and motorcycles. The number of motorcycles with sidecars was half the number of those without sidecars. What could be the maximum number of cars if the total number of wheels on these cars and motorcycles was $115?$
29. If the number of motorcycles with sidecars is $x$, then the number without sidecars is $2x$. Let the number of cars be $y$, then the total number of wheels is $3x + 2x \cdot 2 + 4y = 7x + 4y$. According to the condition, $7x + 4y = 115$, from which

$$
y=\frac{115-7x}{4}
$$

The value of $y$ is greatest when $x$ is smallest. Let $x=1$, then $y=27$. Therefore, the maximum number of cars is 27.