A geometry app shows lengths that add up to 27.4 units.
The Pythagorean theorem can be used to find the lengths of the segments. Each length is the square root of the sum of squares of the difference in x-coordinates and the difference in y-coordinates.
segment AB: length = √(3²+8²) = √73 ≈ 8.544
segment BC: length = √(7²+4²) = √65 ≈ 8.062
segment CA: length = √(10²+4²) = √116 ≈ 10.770
Then the total perimeter is the sum of these lengths:
... 8.544 +8.062 +10.770 = 27.376 ≈ 27.4 . . . . units