Pat has two sheets of large, square stamps. One sheet consists of 9 stamps arranged in a 3-by-3 square. (That's 3 stamps by 3 stamps, not 3 inches by 3 inches.) The other sheet consists of 100 stamps arranged in a 10-by-10 square. The stamps on each sheet are separated by perforated creases. All the stamps on both sheets are the same shape and size.
The total length of the creases on the 3-by-3 sheet is 18 inches.
How many inches of creases does the 10-by-10 sheet have?
First, let's take a look at the 3 by 3 sheet of stamps.
There are two vertical creases between the three columns of stamps.
These two creases comprise a total of six vertical stamp-lengths.
Similarly for the two horizontal creases, six horizontal stamp-lengths.
That makes a total of 12 stamp-lengths of creases.
It's given that there are 18 inches of crease in the 3 x 3 sheet.
Therefore these square stamps are 1.5 inches on a side.
Figure the 10 by 10 sheet the same way.
Nine vertical creases, creating 90 stamp-lengths of vertical crease.
Nine horizontal creases, creating 90 stamp-lengths of horizontal crease.
That totals 180 stamp-lengths of crease in the 10 x 10 sheet.
Since each stamp is 1.5 inches on a side, the total length of crease is 1.5 • 180 = 270 inches