Use Heron's Area Formula to Find the Area of the Triangle

Multiple Choice

Use Heron's area formula to find the area of the triangle pictured below, if $a = 8$ inches, $\mathrm { b } = 10$ inches, and $\mathrm { c } = 4$ inches.

A) $\sqrt { 21 }$
B) 16
C) 40
D) $12 \sqrt { 21 }$
E) $\sqrt { 231 }$