The area of a triangle whose sides are $3\text{cm}$, $5\text{cm}$, and $6\text{cm}$ is:

We can find the area of the triangle using Heron's Formula:
$$\text{Area}=\sqrt{s(s-a)(s-b)(s-c)}$$
Where $a=3$, $b=5$, $c=6$, and $s$ is the semi-perimeter:
$$s=\frac{a+b+c}{2}=\frac{3+5+6}{2}=\frac{14}{2}=7\text{cm}$$
Now substitute $s$ back into Heron's Formula:
$$\text{Area}=\sqrt{7(7-3)(7-5)(7-6)}$$
$$\text{Area}=\sqrt{7\times 4\times 2\times 1}$$
$$\text{Area}=\sqrt{56}=\sqrt{4\times 14}=2\sqrt{14}{\text{cm}}^2$$