How is the formula for calculation in row/column major obtianed?

Question

In my book, this formula is given for calculation of address of row major order's element $[I,J]$:

Address of $[I,J]$th element in row major order $= B + W[n(I-L_r)+ [J-L_c]]$

where B denotes base address, W denotes element size in bytes, n is the number of columns; $L_r$ is the first row number, $L_c$ is the first column number.

A similar formula is given for address in column major order.

I would like to know how this formula is obtained.