A sequence of figures is formed using tiles. Each tile is an equilateral triangle with side length 7 \mathrm{~cm}. The first figure consists of 1 tile. Each figure after the first is formed by adding 1 tile to the previous figure. The first four figures are as shown:
How many tiles are used to form the figure in the sequence with perimeter 91 \mathrm{~cm} ?
Answer Choices
A. 6
B. 11
C. 13
D. 15
E. 23