1st. Let's find the area of the grid:
Each square represents 20 in². There are 45 squares, so:
[tex]A=20\cdot45=900in^2[/tex]The area of the shaded region will be the area of the grid minus the area of the number of squares which are not shaded, so:
[tex]\begin{gathered} A_s\approx900-(15\cdot20) \\ A_s\approx900-300 \\ A_s\approx600in^2 \end{gathered}[/tex]