From the graph:

The library of congress has 28.7 millions of volumes.

The Harvard University has 14.7 millions of volumes.

Let n represent the number of more volumes the library of congress had  than the

Harvard University.

Write the verbal expression to represent the situation.

Rewrite the equation:

According to subtraction property of equality: Subtract 14.7 from each side.

    (Apply commutative property of addition: )

                           (Apply additive inverse  property: )

                                   (Apply additive identity  property: )

                                  (Subtract: )

The library of congress has 14 more millions of volumes than the Harvard University.