4a.
So one property of a rhombus is that all sides are congruent to each other. Using this information, we just need to divide the perimeter by 4, in which the quotient is 6. In short, the measure of FI is 6 units.
4b.
Another property of a rhombus is that opposite angles are congruent and that their diagonals bisect the angles. Since we see ∠HIJ is 72°, just multiply it by 2 to get the measure of ∠FGH. The measure of ∠FGH is 144°.