Question

How can I find the shaded area (blue)?

Answer 1

now PROPERTY : triangle with same base and height have equal area(you can derive it yourself very easy)
now triangle with same areas have been marked as (1,1) (2, 2)...etc

now area of triangle(4) + tri(1) = 32
tri(2) + tri(3) = 16
tri(3) + tri(4) = 20
and tri(1) + tri(2) = ?
so just add eq 1 & 2 and sub(3) to get the expression required

any problem persists do ask