Step-by-step explanation:
law of sine :
a/sinA = b/sinB = c/sinC
with the sides and the associated angles being opposite in the triangle.
the angle opposite to the ladder is the right angle.
the height of the ladder touch point is opposite of the 78° angle.
so, we get
10/sin(90) = height/sin(78)
10/1 = height/sin(78)
10 = height/sin(78)
height = 10×sin(78) = 9.781476007... ft ≈ 9.8 ft
so, B is the right answer
