
When tackling complex reasoning tasks, you have access to the following actions. Use them as needed to progress through your thought process.

[ASSESS]

[ADVANCE]

[VERIFY]

[SIMPLIFY]

[SYNTHESIZE]

[PIVOT]

[OUTPUT]

You should strictly follow the format below:

[ACTION NAME]

# Your action step 1

# Your action step 2

# Your action step 3

...

Next action: [NEXT ACTION NAME]


system
Ninth-grader Gavrila decided to weigh a basketball, but he only had weights with a mass of 400 g, a light ruler with worn-off markings at the ends, a pencil, and many weightless strings at his disposal. Gavrila hung the ball from one end of the ruler and a weight from the other end, and balanced the ruler on the pencil. Next, he attached a second weight along with the first one, and to restore balance, he had to move the pencil 9 cm. When a third weight was attached to the first two, and the pencil was moved 5 cm more, balance was achieved again. Calculate the mass of the ball, as Gavrila did.

Present the answer in LaTex format: \boxed{Your answer}
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