Final answer:
The number 9,648 in expanded form is correctly represented as nine thousand, six hundred forty-eight, which breaks down the value of each digit in the number based on its place value.
Step-by-step explanation:
The question pertains to the concept of expanded form in mathematics, where a number is expressed according to the value of each digit. When we represent a number in expanded form, we write it as the sum of each digit multiplied by its place value. For instance, the number 9,648 would be broken down into 9000 + 600 + 40 + 8.
Thus, the correct expanded form of the number of steps Marcel walked, if that number is 9,648, is 'nine thousand, six hundred forty-eight'. Here the value of each place -- thousands (9,000), hundreds (600), tens (40), and ones (8) -- is specified. This concept is crucial as it helps in understanding the value of each digit within a larger number, and is a primary skill in number operations and place value systems.