help with polygon

The side length of each of the equilateral triangles is 1. 

We see that 2 of such side lengths almost make the side length of the larger square, but there's still a little gap.

Each gap is half of a equilateral triangle, or a 30-60-90 triangle, and the length we want is $\frac{1}{2}$.

So the side length of the larger square is $2+\frac{1}{2}=\frac{5}{2}$.

The area is $({\frac{5}{2}})^{2}=\frac{25}{4}$. So the area of the larger square is 25/4.