Hey there!!
Basic formula :
... a² - b² = ( a + b ) ( a - b )
Equation given :
... 81x² - 25
... ( 9x )² - ( 5 )²
... ( 9x + 5 ) ( 9x - 5 )
Hope it helps!!
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<em><u>The equation can be used to find the actual length of Gregory's room is:</u></em>

<em><u>Solution:</u></em>
Given that,
The scale that he uses is:
1 cm : 4 feet
On this drawing, the room is 3 cm long
Let "x" be the actual length of room
Therefore,
1 cm : 4 feet
3 cm : "x" feet
This forms a proportion. Therefore,

Therefore, Option C is correct
Given that,
Rob chose A as the correct answer. Which is,

But option A is wrong
So, Rob made a mistake in measuring the equivalent ratio, it should be 
Answer:
9:5
Step-by-step explanation:
I think it's 9:5 sorry if I'm wrong.
87.93
eighty seven and ninety-three hundreths