The numerical expression 3/7 + (-7/8) = -25/56 shows that—

The expression shows the addition of two rational numbers 3/7 and -7/8, resulting in another rational number -25/56. This demonstrates the closure property of rational numbers under addition - the sum of two rational numbers is always a rational number. Closure property states that performing an operation on members of a set always results in another member of the same set.