
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
In a sequence of similar geometric diagrams, each larger than the last, the number of shaded smaller units forms a geometric sequence. In the first diagram, there is 1 shaded unit out of 4 total units. In the second diagram, there are 3 shaded units out of 16 total units. If this pattern continues, where the number of shaded units quadruples and the total units quadruple with each new diagram, determine the number of shaded units in the fourth diagram.

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