Using a system of equations, it is found that the cost of a t-shirt is of $3 and the cost of a notebook is of $5.
<h3>What is a system of equations?</h3>
A system of equations is when two or more variables are related, and equations are built to find the values of each variable.
The variables are given as follows:
- Variable x: Cost of a t-shirt.
- Variable y: Cost of a notebook.
Considering the costs of the purchases of Clubs A and B, the matrices give the equations as follows:
- x + y = 8 -> y = (8 - x).
Hence, replacing the second equation into the first:
3x + 2(8 - x) = 19
x = 3.
y = 8 - x = 8 - 3 = 5.
The cost of a t-shirt is of $3 and the cost of a notebook is of $5.
More can be learned about a system of equations at brainly.com/question/24342899
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Given that,
Shelley's pet food store sold one customer 5 peanut butter biscuits for $3. She sold another customer 7 beef treats for $4.20.
For peanut, the cost is ratio is

For beef, the ratio is

If we take cross product of these items,

It implies, that the sale is in true proportion. From the cross product, we find that it is equal.
The answer to the question they gave you is D
Answer:
E D C are the answers for the questions