Answer:

Step-by-step explanation:
To solve this problem, we make use of the geometry that forms between the wall, the floor and the ladder. A rectangular triangle is formed due to the right angle on the wall, <u>see attached image</u>.
We use the cosine function
Where
is the angle, in this case is equal to:
.
is the adjacent side to the angle of 75:
, and
is the hypotenuse of the triangle that is the length of the ladder, so in the last equation we clear for 

and substituting known values:



The length of the ladder is 