15
27
42
72
Plug in the number for “n” then solve: minus 1 times 3 then plus 15
Answer:
ab² - 9
Step-by-step explanation:
Given in the question an expression
(ab + 3)(ab - 3)
To product mentally we will use polynomial identity called
Difference of squares
<h3>a² - b² = (a+b)(a-b) </h3>
here a = ab
b = 3
(ab + 3)(ab - 3) = ab² - 3² = ab² - 9

First some simplifying:

Then with
and
, we have
and
, so

5(x+y)= 20+ 3x
5x+5y=20+3x
5x+5y-3x=20+3x-3x
2x+5y=20
2x+5y-2x=20-2x
5y=-2x+20
5y/5=-2x/5+20/5
y=-2/5x+4
ANSWER: y=-2/5x+4