To find the volume of a cone, you can use the formula:
\[ V = \frac{1}{3} \pi r^2 h \]
where \( V \) is the volume, \( r \) is the radius of the base, and \( h \) is the height of the cone.
Given:
- The diameter of the cone is 12 feet, so the radius \( r \) is half of the diameter:
\[ r = \frac{12}{2} = 6 \text{ feet} \]
- The height \( h \) is 15 feet.
Now, plugging these values into the volume formula:
\[ V = \frac{1}{3} \times 3.14 \times (6^2) \times 15 \]
Calculating \( (6^2) \):
\[ 6^2 = 36 \]
Now substitute back into the formula:
\[ V = \frac{1}{3} \times 3.14 \times 36 \times 15 \]
Calculating \( 36 \times 15 \):
\[ 36 \times 15 = 540 \]
Substituting again, we have:
\[ V = \frac{1}{3} \times 3.14 \times 540 \]
Calculating \( 3.14 \times 540 \):
\[ 3.14 \times 540 = 1695.6 \]
Now, divide by 3:
\[ V = \frac{1695.6}{3} = 565.2 \]
Rounding to the nearest tenth, the volume of the water tank is:
\[ \boxed{565.2} \text{ cubic feet} \]