So, we will be using properties from equilateral triangles and the law of cosines. Buckle up! :)
In the drawing you can see all the information provided. Especially, the information regarding the triangle AED tells us it is an equilateral triangle (a triangle where all the sides are of the same length).
These triangles ALWAYS have 3 times the same angle which is 60*.
This means we can use the law of cosines as we have two sides and the inscribed angle (at the corner A) given. Now the law of cosines tells us that:
x = sqrt( AB^2 + AC^2 - 2*AB*AC*cos(y))
Plugging the given numbers gives us
x = sqrt( 33^2 + 21^2 - 2*33*21*cos(60*))
A calculator tells us that
x = 28.931 so not actually an integer.
Well I do not know where the mistake is :)