You're original equation has a -81, so the factored form will have to have a positive and negative multiplying one another to achieve that...
f(x) = x(x + 9)(x - 9)
In similar figures, the ratio between corresponding sides are the same.

Simplify the two to see that they are equal.
The top and bottom of the left fraction are divisible by 5.
The top and bottom of the right fraction are divisible by 7.

Of course, the dimensions of that third picture would have to be this fraction.
Let's test these answers.

⇒ A is not a solution

⇒
B is the solution
(divide the top and bottom by 6)
Answer:
x=60°
Step-by-step explanation:
angle 135° and (2x+15)° are corresponding and thus are equal
Therefore (2x+15)°=135°
2x=135-15
2x=120°
X=60°
Answer:
5/V2=2.5×V2
Step-by-step explanation:
This is an isoscelle right triangle:
x²+x²=5²
2x²=5²
x=5/V2=5×V2/2=2.5×V2
where V2=sqrt(2)
Answer:
6 1/3 divided by 2 1/2 = x
Step-by-step explanation:
Hope this helps.