Answer:
148
Step-by-step explanation:
Average = sum of numbers /total numbers
let x = 5th number
123.2 = (118+ 128 + 124,+ 98 + x) / 5
123.2 = (468 + x) / 5
Multiply both sides by 5
616 = 468 + x
x = 148
First we need the distances of the sides of the polygon, because perimeter = sum of all sides.






Now, we add all sides for the perimeter:
p = d1 + d2 + d3 + d4 + d5
p = 3+5+5+3+4 = 20 units
I believe that the answer is speed in this situation but I'm not 100% sure