Length of the walking trail is 12 units. 
Step-by-step explanation:
Three points of the walking trail are R(-1,4),S(5,4)and T(5,-2). so we have to calculate the distance between points R and S and also between S and T. finding the sum of these distances would give the distance of the walking trail. 
The equation to calculate the distance between two points 
 and
 and 
 is
 is 

RS= 

=

ST= 
 
 
=

length of the walking trail = RS+ST= 6+6 =12