30 * 30+ 16 * pi * 10 = 900+ 160 * pi

(900+ 160* pi) *20

(pi is 3. 14) is equal to 1 1848 (square decimeter).

2

30* 10=300 16*3. 14* 16=803.84 (803.84+300)*20=22076.8

three

The doctor's hat consists of a square on the top and a column (that is, a rectangle) with no bottom and no cover.

Square area S 1=30cm*30cm=900cm2.

Rectangular area S2=L (perimeter) * h = ∏ d * h = 3.14 *16 *10 = 502.4cm2.

Then a doctor hat needs 900+502.4 =1402.4cm2 =14.024 square decimeter.

Then 20 doctor hats need black cardboard, which is 20* 14.024=280.48 square decimeter.