The expression "B (5 1/2)" seems to indicate the measurement of something, typically in inches or in another context where dimensions are relevant. If "B" represents a specific variable, such as a side length or some other dimension, then "5 1/2" likely refers to 5 and a half units of that measurement.
In fractional terms, 5 1/2 can be represented as 5.5.
If you were asking for something else or a specific context for this expression, please provide additional details!