6. To guard the object, the client agreed with the guards on the following: all of them will indicate the time intervals of their proposed shifts with the only condition that their union should form a predetermined time interval set by the client, and he will choose any set of these intervals that also satisfies the same condition, and pay for the work at a rate of 300 rubles per hour for each guard. What is the longest time interval the client can set to ensure that he definitely stays within 90000 rubles?
6. $\frac{90000}{2 \cdot 300}=150 \text{h}$.