$\"\"$

Let x be the distance between surface and bottom of mine in kilometers.

The temperature of the surface is $\"\"$ and the temperature of the air at the bottom is $\"\"$ .

The temperature increasing per one kilometer is $\"\"$ .

Therefore, the above situation represent the equation is $\"\"$ . $\"\"$

Solve the equation $\"\"$ for x.

Subtract 18 from each side.

$\"\"$

Divide each side by 10.

$\"\"$

Cancel common terms.

$\"\"$ . $\"\"$

The distance between surface and bottom of mine is 2 kilometers.