3. 14×6× 12=226.08 (square centimeter)

3. 14×(6÷2)

6÷2=3 gives =3. 14×3.

3×3=9 gives =3. 14×9.

=28.26 square centimeters

226.08+28.26×2=282.6 (square centimeter)

②

3. 14×40×3=376.8 (square centimeter)

3. 14×(40÷2)

=3. 14×20, which is obtained by 40÷2=20.

=3. 14×400, which is obtained by using 20×20=400.

= 1256 cm2

376.8+ 1256×2=2888.8 (square centimeter)

③

3.14×18×15 = 847.8 (square centimeter)

3. 14×( 18÷2)

Use 18÷2=9 to get =3 14×9.

9×9=8 1 gives =3. 14×8 1.

=254.34 square centimeters

847+254.34×2= 1355.68 (square centimeter)