Find the area of a triangle with sides lengths 17, 18, and 21.4 units. round the answer to the nearest hundredth.

To calculate for the area of the triangle given all its side, use the Heron's formula which is, 
 
                            A = sqrt ((s)(s - a)(s - b)(s - c))

where A is the area. a, b, and c are the measure of the sides and s the semi - perimeter or half of the perimeter.

With the given above, s = (17 + 18 + 21.4) / 2 = 28.2

Substituting the known dimensions to the Heron's formula,
          
          A = sqrt ((28.2)(28.2 - 17)(28.2 - 18)(28.2 - 21.4)) = 148 units^3

Thus, the area of the triangle is 148 units^3.