Four years after a house was constructed, a patio was added. How old, in years, is the patio if the house is x years old?

Answer 1

So, let's use a real number. The house is 9 years old. The patio is then 9 - 4 years old, or 5 years old.

Instead, the patio is x - 4 years old. We can't subtract the two to get a result unless we are given a value for x, which we are not.