First, what do you mean by "#1" ??
Second, with which do you need help?
Lets start with #16.
I guess that p=19 beacuase i cant see the whole paper..
if p=19 this means that: 4+4+3+3+x=19
x is unknown so we need to find the perimeter by add all the sides together and solve for x
Try the other ones yourself by adding in #17 and sovle for x in #18