You could you session scope to accomplish this.
(b.jsp)
session.setAttribute("value",value);
(c.jsp)
session.getAttribute("value");
However, I would recommend doing some major restructuring instead. In your example, the value of your data depends on the order of the elements on the page. If you ever need to re-arrange things (for instance, moving the b.jsp include after the c.jsp include), you risk breaking the business logic.
A good pattern for web development is a model-view-controller pattern. The "controller" determines what page should be displayed, the "model" calculates all the data and makes it available, and the "view" does the display and formatting.
I would recommend reviewing this article, which is helpful for understanding why MVC is a valuable approach:
http://www.javaranch.com/journal/200603/Journal200603.jsp#a5
Edit: As other users have mentioned, request scope would be cleaner than session scope. However, I still recommend determining the value first before writing any display content.