You can put this solution on YOUR website!
It is the special case of rectangle where all sides have same length, which we denote a. There is formula for surface area of rectangle with side a
we can use
now we can use
and we get
which is around 11.873
If you are interested in higher mathematics, area of rectangle can also be computed using definite integral
where a is constant function and integration bounds define left and right side, in our case it would be
= F(b)-F(a) =
whic leads to same result.