What number can go into 42 and 21

He expression 2(l + w) is used to calculate the perimeter of a rectangle, where l is length and w is width. if the length is fraction 2 over 3 unit and the width is fraction 1 over 3 unit, what is the perimeter of the rectangle in units? fraction 2 over 3 unit 1 unit 1fraction 2 over 3 units 2 units

Anyone know? is appreciated! will mark brainliest if correct!

Mrs. gehrke said cheddar weighs 16.8 pounds. he actually weighs 15.2 pounds. what is the percent error?