help

Hint: area of a triangle=(h_b*b)/2

So we can calculate the area in the entire box first which is a 5 by 5 box meaning it has an area of 25(5*5 = 25)

Then we just find the other three right triangles and just find the area of each one of them and then subtract the area from 25.

So the first right triangle is 1*5 = 5/2 = 2.5

second right triangle is 2*4 = 8 /2 = 4

the last one 5*3 = 15/2  = 7.5 

now add these areas together and get 7.5+4+2.5=14. now we do 25-14 = 11. we get 11 as our answer!