Answer :

AL2006

You can write that expression in many different ways,
but you won't find one that's any simpler than (3xy)⁶ .

Here are a few:

(3)⁶x⁶y⁶
729x⁶y⁶
(27x³y³)²
(3x)⁶y⁶
(3y⁶)x⁶