What is the surface area of a rectangular prism with the following dimensions? length: 8 cm width: 13 cm height: 10.5 cm

Height by width face = 10.5 * 13 = 136.50 sq cm height by length face = 10.5 * 8 = 84 sq cmwidth by length face = 13 * 8 = 104 sq cm

Since there are TWO of those faces, we get the total and multiply it by 2.
Total = 324.50 sq cm * 2
TOTAL AREA = 649 sq cm

Source:
http://www.1728.org/recsolid.htm