Since she went south for 2.2 miles
Then she moved 3.5 miles west
Then she moved 5.8 miles south again
To find the distance from the school to the house we will add the 3 distance
To do that mentally we will add 2.2 + 5.8 first
0.2 + 0.8 = 1
Add this 1 to 2 + 5, then
1 + 2 + 5 = 8
Then add 8 to 3.5
8 + 3.5 = 8 + 3 + 0.5 = 11 + 0.5 = 11.5
The distance from the school to the house is 11.5 miles