To find the amount of aluminum needed to refinish the sides of the silo, we need to calculate the lateral surface area of the cylindrical silo. The formula for the lateral surface area \( A \) of a cylinder is given by:
\[ A = 2 \pi r h \]
where:
- \( r \) is the radius of the cylinder,
- \( h \) is the height of the cylinder,
- \( \pi \) is approximately 3.14.
Here, we are given:
- \( r = 4 \) feet,
- \( h = 30 \) feet.
Substituting these values into the formula:
\[ A = 2 \times 3.14 \times 4 \times 30 \]
Now let's calculate it step-by-step:
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Calculate \( 2 \times 3.14 \): \[ 2 \times 3.14 = 6.28 \]
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Calculate \( 6.28 \times 4 \): \[ 6.28 \times 4 = 25.12 \]
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Finally, calculate \( 25.12 \times 30 \): \[ 25.12 \times 30 = 753.6 \]
Therefore, the total lateral surface area of the silo, and the amount of aluminum needed to refinish it, is:
\[ 753.6 \text{ square feet} \]
Rounding \( 753.6 \) to the nearest tenth gives us:
\[ \boxed{753.6} \text{ square feet} \]