That shaded area is equivalent to 3 complete squares shaded out of 7.

So there are 4 unshaded.

As we add unshaded squares, the number of shaded squares remain unchanged at 3 complete squares.

25% (1 unit) —> 3 squares
100% (4 units) —> 12 squares

So we must add 12 - 7 = 5 more unshaded squares.

Area of shaded triangle

= ½ x base x height

Base = 3 sides of a square
Height = 2 sides of a square

So area

= ½ x 3 side of a square x 2 side of a square

= ½ x 6 x (1 side of square x 1 side of square)

= 3 x area of 1 square

= Area of 3 squares



Or


Area of the rectangle = area of 6 squares.

the triangle is half of the rectangle as the diagonal cuts the rectangle into 2 equal parts.

So its area is also half of the rectangle area

6 ÷ 2 = 3

So it has an area of 3 squares