In order to find the angle ∠LHK you take into account that the angle ∠GHK = 180°. Furthermore you have that angle ∠GHL = 79°.
Then, ∠LHK + ∠GHL = 180°
You solve the previous relation for ∠LHK by replacing the value of ∠GHL, just as follow:
∠LHK + ∠GHL = 180°
∠LHK = 180 - ∠GHL = 180 - 79 = 101°
Hence, angle ∠LHK is equal to 101°