A small company has one color printer and one black-and-white printer, each printing at different rates. The color printer, working for 5 minutes and the black-and-white printer, working for 3 minutes print a total of 70 pages. When the black-and-white printer worked for 6 minutes and the color printer worked for 9 minutes, they printed a total of 135 pages. This situation is represented by the equations below, where b represents the number of pages per minute printed by the black-and-white printer and c represents the number of pages per minute printed by the color printer.

How many pages per minute does the black -and- white printer print?

A. 11 B. 12 C. 15 D. 18