Question 1154424
Hope I have interpreted it correctly. If so find the answer.
*[illustration gable.png]

ABC is isosceles triangle. AD is the altitude from A.

AD bisects  BC 

therefore BD = 40
BA = 41 given

In right triangle ABD AB^2 = BD^2 +h^2   ( Pythagoras theorem.

h^2 = AB^2-BD^2

h^2 =81
h=9 ft