It seems like you are referring to the sides of a triangle, where \( C \) and \( B \) are the lengths of two sides. However, to find the length of side \( b \) (which I assume is the same as side \( B \)), I need more information about the context or specific relationships among the sides of the triangle.
If you are referring to the lengths of the sides in a specific triangle and want to use the Triangle Inequality Theorem or some trigonometric relationships, please clarify your question with more details.
If "C side is 30" and "B side is 78" directly indicates \( C = 30 \) and \( B = 78 \), then the value of side \( b \) is simply 78.
If you're looking for a different relationship or formula, please provide that information!