Answer:
Let X be number of days
Let Y be total amount of pages
21x=y
Explanation:
So we know that Arnold reads 21 pages a day
But we don’t know how many days
THe number of pages can change expending on the amount of days he reads
So lets make that y.
So 21x=y is the equation unless they ask for different interpatations of the variables (x,y,z)