
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 the diagram, the grid is made up of squares. What is the area of the shaded region? [asy]

size(9cm);

// Fill area
fill((0, 0)--(0, 3)--(4, 3)--(4, 4)--(9, 4)--(9, 5)--(15, 5)--cycle, gray(0.75));

defaultpen(1);

// Draw grid
draw((0, 0)--(15, 0));
draw((0, 1)--(15, 1));
draw((0, 2)--(15, 2));
draw((0, 3)--(15, 3));
draw((4, 4)--(15, 4));
draw((9, 5)--(15, 5));
draw((0, 0)--(15, 5));
draw((0, 3)--(0, 0));
draw((1, 3)--(1, 0));
draw((2, 3)--(2, 0));
draw((3, 3)--(3, 0));
draw((4, 4)--(4, 0));
draw((5, 4)--(5, 0));
draw((6, 4)--(6, 0));
draw((7, 4)--(7, 0));
draw((8, 4)--(8, 0));
draw((9, 5)--(9, 0));
draw((10, 5)--(10, 0));
draw((11, 5)--(11, 0));
draw((12, 5)--(12, 0));
draw((13, 5)--(13, 0));
draw((14, 5)--(14, 0));
draw((15, 5)--(15, 0));

// Draw lengths
path height = (-0.5, 0)--(-0.5, 3);
path width = (0, -0.5)--(15, -0.5);
path height2 = (15.5, 0)--(15.5, 5);
draw(height); draw(width); draw(height2);
draw((-0.6, 0)--(-0.4, 0));
draw((-0.6, 3)--(-0.4, 3));
draw((0, -0.6)--(0, -0.4));
draw((15, -0.6)--(15, -0.4));
draw((15.4, 0)--(15.6, 0));
draw((15.4, 5)--(15.6, 5));

// label lengths
label("$3$", (-0.5, 1.5), W);
label("$15$", (7.5, -0.5), S);
label("$5$", (15.5, 2.5), E);

[/asy]

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