Can someone explain how to do this? geometry eoc's are tomorrow and i have to know this stuff so answer quickly.

A rule of Polygons is that the sum of the exterior angles must equal 360. 
Remember that for your testing. 
A polygon is where all sides equal the same amount, in your case, 18 degrees.
So divide 360 by 16, equalling D.20
Good Luck!

3.
we can solve it

draw a point for the center
draw lines from the center to each vertex
you get  lots of triangles

see the diagram so it won't be confusing an since I will be refering to stuff in there

striahge line=180
so
18+x+x=180
minus 18
2x=162
divide 2
x=81
now we know 2 interior angles
x and y=81
angles ina triangle add to 180
therefor
x+y+z=180
81+81+z=180
162+z=180
minus 162
z=18

all central angles add up to 360
how man y are there?
18 times how many=360
divide both sidess by 18
how many angles=20
20 central angles=20 sides

4.

we can compare using side to angle ratios
since 9=9 and they share a side, the sides PQ and SR and congruent and PS is congruent to PS
therfor the only different side is QS and PR

ratio is the angles
QS:PR=63:105=3:5

they are in ratio 3:5