Answer: 4.6
Explanation:
GH is equal to 4.6 since it is congruent to JH. GJ is one line, which makes angles GKH and JKH supplementary angles. Since angle GKH = 90, angle JKH must also equal 90, making these triangles similar. However, if you wish to see it done out mathematically, the following explanation is there:

3.6^2 + HK^2 = 4.6^2
HK^2 = 4.6^2 - 3.6^2
HK^2 = 8.2
HK = 2.86
HK^2 + GK^2 = GH^2
8.2 + 12.96 = GH^2
GH = 4.6