A rectangular board is 1400 millimeters long and 900 millimeter wide

In order to find the area in square meters, first convert the length and width to meters:
[tex]\begin{gathered} l:1400mm\times\frac{1m}{1000mm}=1.4m \\ w:900mm\times\frac{1m}{1000mm}=0.9m \end{gathered}[/tex]then, find the area of the board through the formula:
[tex]\begin{gathered} A=l\times w \\ A=1.4m\times0.9m \\ A=1.26m^2 \end{gathered}[/tex]Answer:
The area of the board is:
[tex]A=1.26m^2[/tex]