$\"\"$

Two sightings are taken 4000 ft distance from the base of the tower.

Angle of elevation to the top of the sky pod is $\"\"$ .

Angle of elevation to the top of the tower is $\"\"$ .

$\"\"$

Draw the diagram for situation:

$\"\"$

$\"\"$ represents the distance between the arch and boat on the missori side.

From the figure,

$\"\"$

Substitute $\"\"$ in the above expression.

$\"\"$

$\"\"$ .

$\"\"$

From the figure,

$\"\"$

$\"\"$ ft.

From the figure, $\"\"$ .

$\"\"$

Therefore, the Mississippi river is approximately $\"\"$ wide at St.Louis riverfront.

$\"\"$

The Mississippi river is approximately $\"\"$ wide at St.Louis riverfront.