Question 508956
Ladder = 19.5 ft
distance of base from wall = 7.5 ft
height at which it touches the building = x
They form a right triangle

By Pythagoras theorem 									
Hypotenuse^2 = Leg1^2+leg2^2									
{{{ 	19.5	^2	=	7.5	^2	+	7.5	^2}}}	
19.5	^2	-	7.5	^2	=	x^2			
380.25	-	56.25	=	x^2					
324	=	x^2							
{{{ sqrt(x^2)=		sqrt(	324	)}}}					
x=	18	m