Answer:
57.4
Explanation:
Go to point A and draw a line straight down, perpendicular to HT. Let's label the point where your drawn line hits AT as B. Now you have the line segments HB, BT.
HB + BT = 100
Solve for the height of the triangle, BA.
BA = sin35(80) = 45.9
HB = cos35(80) = 65.5
BT = 100 - 65.5 = 34.5
Now you can solve for AT, which is the hypotenuse of ΔBAT:
(AT)² = 45.9² + 34.5² = 3295
AT = √3295 = 57.4