How do you write a mathematical or variable expression for each quantity: the value in cents if 7 nickels?

Hint: In this question, we have to find the value of 7 nickels. 7 nickels can be written as 1 nickel added to itself 7 times, or it can also be written as 7 times of 1 nickel. So we can find the value of 7 nickels by converting the given statement into mathematical form. As the quantity of nickels has become 7 times, the value of cents equal to one nickel will also become 7 times. Using the above information, we can find out the correct answer easily.

Complete step-by-step solution:
We know that the value of 1 nickels = $5\,cents$
So, the value of 7 nickels will be = $7 \times 5 = 35\,cents$
Hence, 7 nickels are equal to 35 cents.

Note: For solving these types of questions, we take the help of algebra. Algebra is defined as a mathematical expression that contains a combination of numerical values and alphabets. The alphabets represent some unknown quantity; as in this question, the unknown quantity is the value of cents. With the help of algebra, we can make general formulas that make the calculations easier.

Let the number of nickels be x whose value in cents we have to find, we know the value of 1 nickel in cents, so the value of x cents will be x times the value of 1 nickel. With help of this general equation, we can convert any quantity of nickels into cents easily.