Question 194508
Ok the perimeter of a rectangle is 2 times its length plus 2 times its width.
2(Length) + 2(Width) = Perimeter
We are given that the width is 16cm 
and we are asked to find what lengths will give a perimeter greater than 78cm
The words "greater than" tell us that we are dealing with an inequality not an equation. So based on this information we can set up an inequality to solve for values of  length. Lets call the length x
2 times the length which we are calling x Plus 2 times the width which is 16 is greater than 78
2x + 2(16) > 78
next multiply 2 times 16 to get 32
2x + 32 > 78
then subtract 32 from both sides
2x > 46
finally divide both sides by 2
x > 23
So we have found that the length must be greater than 23cm to get a perimeter greater than 78cm