Firstly the coefficient, or the number next to the variable, which is x, goes before it. So instead of x3, it's 3x.
So, to solve to find what x is, you need to divide by 3 on both sides of the equal sign.
3x=729
Dividing by 3 on the left cancels out the 3, leaving just the x.
Dividing the other side gets you what x equals.
x= 243