Ahouse is 25 feet tall and a ladder is set up 35 feet away from the side of the house. approximately how long is the ladder from the ground to the roof of the house

Use Pythagorean Theorem of a^2 + b^2 = c^2 where a and b are the legs of the triangle set up by the house height and the ground, and c is the hypotenuse or how long the ladder is. C is going to be our unknown.
 
Just plugging in you get 25^2 + 35^2 = c^2. Simplify to 625 + 1225 = c^2. Simplify again to 1850 = c^2. The square root both sides to isolate the variable c. C = sqrt(1850) or approximately 43.0116 feet if rounded to 4 decimal places. 

The ladder is approximately 43.0116 feet long.