The altitude of an equilateral triangle is 15. what is the length of each side

The altitude bisects one of the lines of the equilateral triangle and makes an angle of 90 degrees at the intersection.
Let each side of the triangle be x, then: x^2 - (x/2)^2 = 15^2
x^2 - x^2/4 = 225
3x^2/4 = 225
3x^2 = 4 x 225 = 900
x^2 = 900/3 = 300
x = sqrt(300) ≈ 17.32

The answer of the above question is

D. i think it is the savings