This question can be solved using the Herons equation where
A = SQRT [s*(s-a)*(s-b)*(s-c)]
A = area of the triangle
a, b and c are the sides of the triangle
s = (a+b+c)/2
Since we are given the area, we can express "s" as a function of the third side c. This can be substituted in the original equation so as to obtain an expression to solve for the third side c
s = (4+10+c)/2 = (14+c)/2
using the solver function of the calculator or MS Excel, the third side is 7.21 units
