We can measure it by applying Pythagoras theorm..
let the sides of rectangle be A, B, C and D..
Lenght AB ( _____ ) be 8m, Breadth BC( ] )be 6m
Diagonal ( / ) be AC = x
application of theorm..
AC^2 = AB^2 + BC^2
x^2 = 8^2 + 6^2
x^2 = 64 + 36
x = 10m..
so the shortest distance travelled is 10m.