Triangle Alert

Let's divide the figure above become a three triangle ( $A, B$ and $C$ )

Find the area of Triangle $C$

$\frac {4 \times 3}{2} = 6$

Now find the area of Triangle $A + C$

$\frac {4 \times 5} {2} = 10$

So we can conclude that,

Area of Triangle $A$ $= 10-6 = 4$

Now find the area of Triangle $B+C$

$\frac{4 \times 10}{2} = 20$

So we can also conclude that,

Area of Triangle $B$ $= 20-6 = 14$

Green Area $= 14 + 4 = 18$