4. ADEF is an equilateral triangle.
E
24
20
D
F

By Pythagorean theorem
x²+GF²=EF² ( where G is the point of intersection of perpendicular lines)
now, GF=1/2 EF= 12
x²+12²=24²
x²=24²-12²
x²=432
x=√432
x=12√3
x≈20.78