Pat starts with two identical square pieces of paper. On the first one, she draws straight lines that divide the paper into a $3$-by-$3$ grid of squares. The total length of the lines she draws is $18 \text{ cm}.$

On the second piece of paper, Pat draws straight lines that divide the paper into a $6$-by-$6$ grid of squares.

What is the total length of the lines that Pat draws on the second piece of paper?