W=10
Explanation:
First you need to find the area of the triangle. To do that you do BH*0.5
So- 8*6*.5
And you get- 24
So if the area of of the rectangle is 5 times the size of the area of the triangle then you do 5*24 and get 120
And since we know 12 is one of the sides and to find area of a rectangle u do L*W, all you would do is 120/12 and you get 10