3. Usually, schoolboy Gavriil takes a minute to go up a moving escalator by standing on its step. But if Gavriil is late, he runs up the working escalator and thus saves 36 seconds. Today, there are many people at the escalator, and Gavriil decides to run up the adjacent non-working escalator. How much time will such an ascent take him if he always exerts the same effort when running up the escalator?


Solution. Let's take the length of the escalator as a unit. Let $V$ be the speed of the escalator, and $U$ be the speed of Gavrila relative to it. Then the condition of the problem can be written as:

$$
\left\{\begin{array}{c}
1=V \cdot 60 \\
1=(V+U) \cdot(60-36)
\end{array}\right.
$$

The required time is determined from the relationship $1=U \cdot t$. From the system, we get $V=\frac{1}{60} ; U+V=\frac{1}{24}$; $U=\frac{1}{24}-\frac{1}{60}=\frac{1}{40}$. Therefore, $t=40$ seconds.

Answer: 40 seconds.

Criteria: 20 points - complete and correct solution, 15 points - correct approach to the solution, but an arithmetic error is made; $\mathbf{1 0}$ points - the system of equations is correctly set up, but the answer is not obtained; 0 points - everything else.