Tom wants to reach a second floor window on a house that is 20 feet above ground. if he must put the ladder at a 70 degree angle to the ground, how long must the ladder be?

Assuming the house is parallel to the ground, your triangle is made up by the house, the ground, and the ladder. Using sin(x) = opposite/hypotenuse on the angle 70 degrees, you would have sin(70) = 20/x (because 20 is the side opposite of the angle connecting the ladder and the ground)
--> simplify sin(70) * x = 20 --> x = 20 / sin(70 
--> substitute (and make sure your calculator in in degrees) x= 21. 284