There's been a misinterpretation of the question. The ratio is for the areas of the whole rectangle to the shaded area to the whole square instead of just the unshaded parts.


Area of square B = 3 units
3 units = 36 cm²
1 unit = 36 cm² ÷ 3
= 12 cm²


Area of whole figure

= Area of rectangle A + area of square B - shaded area

= 5 units + 3 units - 1 unit
= 7 units
= 7 x 12 cm²
= 84 cm²

The numbers inside the figures would be 4 , 1, 2 instead.

Ah... Yes.
Total area of rectangle A =5u
Total area of square B = 3u
Shaded area = 1u

Whole figure A:shaded: B = 4:1:2
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@Mimi, Refer to J comments for correct answer.

@J Thank you for highlight :)