Let $F_g$ be a field of order $g$, find the order of $D_n({F_g}), B_n({F_g}), SL_n({F_g}), GL_n({F_g})$
Where $D_n({F_g})$=Diagonal matrices, $B_n({F_g})$=Borel subgroup
In the case of $D_n({F_g})$: where have $n$ places on the diagonal when $0$ is not allowed to be used, so we have $(g-1)^n$ options
In the case of $B_n({F_g})$: we have $n^2$ elements in a $n\times n$ matrix, in the diagonal we have $n$ elements so a triangular matrix have in total ${\frac{n^2-n}{2}+n}=\frac{n^2+n}{2}$ elements on the diagonal we have $(g-1)^n$ options and everywhere else $\frac{g^{n^2}+(g-1)^n}{2}$
How should I approach $SL_n({F_g})$ and $GL_n({F_g})?$