#1
Apply pythagorean theorem
So
Diagonal
- √L²+B²
- √12²+9²
- √144+81
- √225
- 15ft
#2
Again apply
- H²=P²+B²
- H²=3²+9²
- H²=9+81
- H²=90
- H=√90ft
- H=9.5ft
This is a problem of Difference-of-squares. We know that for a difference of squares

the factorization is given by:

To learn this you need to remember that a <em>difference</em> means <em>subtraction.</em> So applying those concepts we can solve this problem step by step.
Applying distributive property:

Applying distributive property again:

Simplifying:
<em>The correct answer is C</em>