The lemma is:
Let $M$ be an LBA with $q$ states and $g$ symbols in the tape alphabet. There are exactly $qng^n$ distinct configurations of $M$ for a tape of length $n$.
I want know why LBA has $qng^n$ configurations.
Following is the proof:
A configuration of $M$ is like a snapshot in the middle of its computation. A configuration consists of the state of the control, position of the head, and contents of the tape. Here, $M$ has $q$ states. The length of its tape is $n$, so the head can be in one of $n$ positions, and $g^n$ possible strings of tape symbols appear on the tape. The product of these three quantities is the total number of different configurations of $M$ with a tape of length $n$.