Final answer:
In algebra, a number with a fixed value that does not change, like 5, 9, or 20, is called a constant. It is different from a variable, which can take various values, or a coefficient, which multiplies a variable. Constants are the correct answer to what these numbers are called.
Step-by-step explanation:
In algebra, numbers like 5, 9, 20, which have fixed values and do not change, are called constants. These are distinct from variables, which are symbols like x and y that can represent various numbers in different situations. For example, in the equation 'a + b = c', if 'a' and 'b' are known constants, and 'c' is the sum of those numbers, then 'a' and 'b' do not change. However, 'x' in 'mx + b = y', when solving for 'y', is the independent variable that can take on different values. The number 'm' would be a coefficient, which is a constant that multiplies the variable 'x', and 'b' is also a constant that is added or subtracted in the equation. In this context, the correct answer to the student's question is option b) Constant.