3/6 (r-7) =1 The answer is r=7
Well, the formula for simple interest is

"I" is interest, "p" is the principal, "r" is the rate, and "t" is the time.
If you substitute the numbers, you get

When you multiply them together, you get

So, the simple interest for 3.5 years is $210.
But, in order to get the total balance, you have to add the interest and the principal together.

So, the balance after 3.5 years is $1,210.
It’s goes by 7.5
Just by looking at the chart you can see x-axis to y- axis for example, point for 2 ,you can divide to find out the answer. So it’s 7.5
Let
x---------> the length side of the rectangular area
y---------> the width side of the rectangular area
we know that
the area of the rectangle is equal to

-----> equation 
The perimeter of the rectangle is equal to

but remember that the fourth side of the rectangle will be formed by a portion of the barn wall
so
-----> equation 
<em>To minimize the cost we must minimize the perimeter</em>
Substitute the equation
in the equation 
![P=x+2*[\frac{200}{x} ]](https://tex.z-dn.net/?f=%20P%3Dx%2B2%2A%5B%5Cfrac%7B200%7D%7Bx%7D%20%20%5D%20)
Using a graph tool
see the attached figure
The minimum of the graph is the point 
that means for 
the perimeter is a minimum and equal to 
<u>Find the value of y</u>



The cost of fencing is equal to

therefore
<u>the answer is</u>
the length side of the the fourth wall will be 