How do we evaluate algebraic expresions?

Write each expression another way;

1) (12x) 12(x)
2)(4/y) 4÷y
3)(3xy/2) 3•x(y÷2)

The difference between variable and a constant because a variable is a letter represents a number that can vary. A constant is a number that could not change. So a constant doesn't change but a variable can change because it gets replace for a number.