Answer:
x-4=y
Step-by-step explanation:
9-4=5
12-4=8
If you assign variables to the problem, it can make things a lot simpler. Lets say chairs are x and tables are y. Therefore you have:
2x+6y=40
5x+3y=25
Now you can isolate the variable of one equation and put it into another (it doesn't matter which. I'm going to manipulate the top equation to plug into the bottom one).
2x=40-6y
x=20-3y
Now I plug into bottom equatioin:
5(20-3y) + 3y=25
100-15y+3y=25
100-12y=25
-12y=-75
y=$6.25
Now you can plug in y in either equation to get x.
2x+6(6.25)=40
37.5+2x=40
2x=2.5
x=1.25
So it costs $6.25 for each table and $1.25 for each chair. If you think about it, it would make sense for the table to cost more for the chair.
She made her mistake at the first step. To simplify a radical, you would find two numbers that multiply by each other to get your original number (under the radical)
and have one of the number be a perfect square.
Her reasoning is wrong because 10*10 is not

. Had she been correct, her answer should have been able to be squared to equal

In other words, she should have done

(We used 25 because 25 is a perfect square, 5*5=25).
:)