you can use Heron Formula in the calculator to output the result, but i still show you the steps on paper thro
lengths of the 3 lines: \sqrt{392} , \sqrt{676} , \sqrt{676}
s= (\sqrt{392} + \sqrt{676} + \sqrt{676})/2=35.89949494
area= \sqrt{s(s- \sqrt{392} )(s- \sqrt{676})^2 } =238