Area of a square with side s is [tex]\sf{s^2}[/tex]
In your question, the side or s is: [tex]\sf{8x^7y^3}[/tex]
And so the area of a square with that side length would be:
[tex]\sf{(8x^7y^3)^2}[/tex]
And using this formula: [tex]\sf{(a^b)^c =a^{b\times c}}[/tex]
We get that the area is:
[tex]\sf{(8x^7y^3)^2 = 8^2 x^{7\times 2} y^{3\times 2}}[/tex]
And simplifying that we get the final answer as:
[tex]\huge{\boxed{\bf{Area=64x^{14}y^{6}}}}[/tex]