since when you multiply two negative numbers for example -15 times a negative 14 your answer will be positive then you do 15 times 14 which gives you positive 210.
If we look at ΔBDH, we notice that m∠BHG has to be 108 - 36 - 39 = 105°. Because x and ∠BHG are a linear pair we know that x = 180 - ∠BHG = 180 - 105 = 75°.
