You can visualise one half of the S figure as a 3/4 circles.
Then you have find the perimete and times 2

Outer cirlce – 2(3.14)20 X3/4 = 94.2cm
Inner circle – 2(3.14)10X3/4 = 47.1

a) Total perimeter = (94.2 + 47.1 + 10) X 2= 302.6cm ##

b) If you look at the above picture, it’s actually made up of 3 sets of identical quadrants, or 6 sets of identical quadrants to form a S

So we just find the unshaded area of one quadrant and mulitply by 6.

Area of 4 squares = 20X20 = 400 cm²
Area of outer quadrant = (Pi X 20X20) / 4 = 314 cm²
Unshaded area at quadrant’s corner = 400 – 314 = 86cm²

UNshaded inner quadrant = (Pi X 10 X 10)/4 = 78.5 cm²
Total unshaded quandrant = 86 + 78.5 = 164.5 cm²

#Amendment notes: Forgot to add on 4 more unshaded squares highlighted with tick.#

Total unshaded area for the whole figure = 164.5 X 6 + 400= 1387 cm² ###

Ref: http://www.kiasuparents.com/kiasu/forum/viewtopic.php?p=1691591#p1691591