Question 143413
Presuming the wall is perpendicular to the ground (not necessarily a reasonable assumption in real life but in the fantasy world of algebra and trigonometry word problems perfectly fine), then you would have a right triangle where the length of the ladder is the hypotenuse and the distance of the base of the ladder from the wall is the length of the side adjacent to the desired angle.


We know that {{{cos(alpha)=adjacent/hypotenuse}}}, so you need to calculate {{{arccos(3/20)}}}


Put your Windows Calculator app into Scientific mode (view menu).  Click 3, /, 20, =, check the Inv box in the upper left, then click the cos button.  Then round off appropriately.


But then again, that is just me...some people would walk up to the ladder with a protractor and say "hmmm, about 81 degrees, give or take"