8.B So lets look at the possibilities we wrote and see how many have a sum of 7. (1,1) (1,2) (1,3) (1,4) (1,5) (1,6) (2,1) (2,2) (2,3) (2,4) (2,5) (2,6) (3,1) (3,2) (3,3) (3,4) (3,5) (3,6) (4,1) (4,2) (4,3) (4,4) (4,5) (4,6) (5,1) (5,2) (5,3) (5,4) (5,5) (5,6) (6,1) (6,2) (6,3) (6,4) (6,5) (6,6)
So out of 36 possibilities, 6 of them have a sum of seven P(sum of 7)=6/36 simplify to 1/6
If you make a table you can see that L_1 + L_2 gets larger as you increase theta prom pi/2 and decrease theta from pi/2. This means that pi/2 is the theta that will yield the smallest length for the ladder. Plugging this into L_1 + L_2 you get 19.8 (rounded to the nearest hundred)