For the ladder and wall height question use Pythagoras theorem. The hypotenuse squared of a right angled triangle equals the sum of the other two sides squared. A wall is vertical and will create a right angle with the ground, which is horizontal (in this case). So ladder squared = wall squared plus 3 squared.
Wall squared = ladder squared minus 3 squared
Wall squared = 10 x 10 - 3 x 3
Wall squared = 100 - 9
Wall squared = 91
Wall = square root of 91
Wall = 9.539392014
Wall = 9.54 ft (to nearest hundredth)