If \(a=b\), then \(b\) can be substituted for \(a\) in any expression or equation.
In words: A quantity can be replaced by a quantity of equal value in any expression or equation.
Example:
If \(m = 2\) and \(m + 4\), then \(2 + 4\).
If \(y = x\) and \(x - 5 = 7\), then \(y - 5 = 7\).
If \(j = 2k\) and \(j + k = 11\), then \(2k + k = 11\).