Cut off the central angle by 3/ 10, that is, cut off the circumference by 3/ 10.

40× 3/10 =12cm

2、 120÷360= 1/3

Cut off the central angle of 1/3, that is, cut off the circumference of 1/3, that is,

56.52÷ 1/3, with a radius of:

56.52÷ 1/3÷3. 14÷2

= 169.56÷3. 14÷2

=27 cm

3.AB is a semicircle with a circumference of 40×3. 14= 125.6 cm.

Arc length of arch bridge:125.6÷ 2 = 62.8cm.