Height of the trapezoids = sqrt (17^2 - 8^2) = 15cms
base = 19 cms
(b) area of each trapezoid = 15/2 (35 + 19) = 405 cm^2
Total area painted blue = 2*405 = 810 cm^2
(c) length of the edges of one trapezoid = 35 + 19 + 2(17) = 88 cms
So one piece of sandpaper ( can sand up to 80 cm) will not be enough to sand all of the edges.
The area formula of a triangle is 1/2 ×base ×height
so 1/2×3 in ×8 in ---> 1/2×24 in = 12 in