Answer:
3 millimeters
Explanation:
The formula for finding perimeter: 2W+2L=P
W= width
L= length
P= Permiter
So just substitute the numbers in the equation
4 millimeters is the width
14 millimeters is the perimeter
So this is your equation
2*4+2L=14
8+2L=14
Subtract 8 from both sides
2L=6
Divide both sides by 2
L=3
So your length is 3 millimeters
To check:
(2*4)+(2*3)=14
8+6=14
14=14