mock 14,sbi po,no.41,,i cant understand this concept.

Hi Kritika
The mentioned question is based on properties of similar triangles.
If two triangles are similar then the ratio of their areas is equal to the square of the ratio of their sides.
Here triangle APQ is similar to triangle ABC. If you take the area of unshaded region to be x, then
1/4 = x/x+225 => 3x= 225 => x = 75. So the area of ABC is 225 + 75 = 300.
Hope it clears your doubt. If any doubt persists please post it again.
Thanks.