This is classical probability, so the probability of an event is the number of "favorable" events over total events.
The total number of events, by the counting principle, is 2^3=8. The total number of events remains the same for P(H,H,H) and P(H,T,H), as you're still flipping 3 coins with two sides.
For P(H,H,H) the favorable event is (H,H,H) so 1, for P(H,T,H) the favorable event is (H,T,H) also one.
angle 3 and angle 4 are equal because the diagonals/2 are equal. Angle 4 equals angle 1 due to opposite interior angles thereom. 90 degrees minus 37=53 degrees which is angle 2. Since angle 2 is equal to the angle GKH, 53+53=106 and 180-106=74 degrees, and due to vertical angles, angle 7 is 74 degrees.