How do you determine if 2/3 is greater than 7/8

The smaller denominator will give a larger fraction. Another method for comparing is to think of the fractions. In this example it is obvious that 1/3 is smaller than 7/8. For one thing, 1/3 is smaller than 1/2 and 7/8 is larger than 1/2.
so therefore 2/3 is not greater than 7/8
2/3 only equal .66
7/8 equals .875

You have 2 sides that are 2 cms and you have 6 sides that are 1/2 cm and you have 4 sides that are 1 cm. the smallest sides are 1/2 the medium sized sides are 1 and the smallest are 1/2. so to find the perimeter you have to add them all up together so your answer will be 11 cm's