I do not know which formula to use however, i think its the top/green one Rashawn bought a CD that cost $19.99 and paid $21.56, including sales tax.What was the rate of the sales tax

It's the first one.

Step-by-step explanation:

Using the formula, Total Cost = Purchase Price + Sales Tax,

Let x be the sales tax

$21.56 = $19.99 + x

At this point, it's very easy to do this. To find x, you subtract $19.99 from the total cost or $21.56.

$21.56 - $19.99 = $1.57 hence the sales tax is $1.57.

How can we check our answer?

If you aren't sure if you are correct, just add the purchase price with the sales tax.

$19.99 + $1.57 = x

$19.99 +$1.57 = $21.56

It is the same as the Total Cost so $1.57 is your correct answer.

It asks for the rate, not the sales tax. Continuing with this, to find the rate, you do Sales Tax/Purchase Price = Rate of Sales Tax/100%

1.57/19.99 = x/100%

Cross multiply: 19.99*x = 1.57*100

19.99*x = 157

Then, do

19.99*x/19.99 = 157/19.99 which is equal to 7.85392696%, round that to 7.85%

So the rate of the sales tax is 7.85%

those are the answers