First, let's find the measure of the third side, using the law of cosine:
[tex]\begin{gathered} a^2=b^2+c^2-2bc\cdot\cos(A)\\ \\ a^2=76^2+39^2-2\cdot76\cdot39\cdot\cos81°\\ \\ a^2=5776+1521-927.34\\ \\ a^2=6.369.66\\ \\ a=79.81 \end{gathered}[/tex]Now, let's use Heron's formula to calculate the area:
[tex]\begin{gathered} p=\frac{a+b+c}{2}=97.405\\ \\ A=\sqrt{p(p-a)(p-b)(p-c)}\\ \\ A=1463.75 \end{gathered}[/tex]