Answer:
9
Step-by-step explanation:
perimeter= side+side+side+side
if we know that it is 4 millimeters tall, we know two sides are 4 millimeters tall, so we have 8. to find the sum of the last two sides, we subtract 8 from 26, which give us 18. finally, we divide by 2 to get 9, the width of the rectangle.
