Question 512876
let the foot of the ladder be located at M

let the distance on ground from ladder foot to base of building A be MA

let the distance on ground from ladder foot to base of building B be MB

MA^2= 13^2-12^2
MA^2= 169-144=25
MA=5 m
...
MB^2= 13^2-8^2
MB^2=169-64
MB^2= 105
MB= 10.25 m

MA + MB =  alley width

5+10.25= 15.25 m 
    
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