You just have to add I think
By Green's theorem,

where
is the circle
and
is the interior of
, or the disk
.
Convert to polar coordinates, taking

Then the work done by
on the particle is

Answer:
Step-by-step explanation:
Perimeter = 2(l + w)
l = 8.5cm, perimeter = 24cm
24 = 2(8.5 + w)
Dividing through by 2
24/2 = 8.5 + w
12 = 8.5 + w
W = 12 - 8.5
W = 3.5cm