Explanation:
Since we have given that

Now, we have to prove it as

Now, start the iterations:

So, first blank will be filled with

Second blank will be filled with

Hence proved.
First you solve for y.
5x+ y= 12 so Y= 12-5x
And plug it into the next equation
3x- 3(12-5x) = 18
Distribute
3x-36+15x=18
Add 36 to both sides
3x+ 15x= 54
18x= 54 ... divide
x= 3
And you can plug in x to solve for Y
5(3) + y = 12
15+ y = 12 ...subtract 15 from both sides
y= -3
"Less than" means subtraction
The order they appear in tells me to subtract 9 from N.
n - 9