First, we're looking for the length of hypotenuse of right triangle, use pythagorean theorem. We'll get the square of hypotenuse by adding the square of perpendicular sides. See image attached.
h² = 3² + 4²
h² = 9 + 16
h² = 25
h = √25
h = 5
The hypotenuse is 5 meters
Second, count the total distance
d = bryce to warren + warren to mark + mark to bryce
d = 4 + 5 + 3
d = 12
The paper airplane has traveled 12 meters