we have that
In a rhombus the length sides are congruent
the diagonals bisect each other and are perpendicular
so
If mmIn the right triangle IFJ
mtan(30)=FJ/IJ
Remember that
FJ=4
substitute the given values
Find the length side IF
Applying Pythagorean Theorem
IF^2=4^2+IJ^2
IJ^2=48
IF^2=16+48
IF^2=64
IF=8 units
that means
side GH=8 units
side JG=side IJ=4√3 units
side FH=2*side FJ=2*4=8 units