4. (10 points) The figure below is the front view of a solid structure made up of several blocks, each 12 cm long, 4 cm wide, and 2 cm high. Several points are marked on it. An ant starts from the left side of the ground, passes through the marked points, and reaches the right side of the ground. If the ant's upward climbing speed is 2 cm per second, downward climbing speed is 3 cm per second, and horizontal crawling speed is 4 cm per second, then the ant will take at least $\qquad$ seconds to complete its journey.
【Analysis】From the figure, we can see: First, let the ant crawl up one length, then crawl horizontally 5 widths, then crawl down one length, then crawl horizontally 2 lengths, crawl up 1 length, then crawl horizontally 5 widths, and finally crawl down 1 length.

【Solution】Solution: The crawling route is as shown in the figure:
$$
\begin{array}{l}
(5 \times 4 \times 2+2 \times 12) \div 4 \\
=64 \div 4 \\
=16 \text { (seconds) } \\
12 \times 2 \div 2=12 \text { (seconds) } \\
12 \times 2 \div 3=8 \text { (seconds) } \\
16+12+8=36 \text { (seconds) }
\end{array}
$$

Answer: The ant has crawled for at least 36 seconds.
The answer is: 36.