60:80=X:40

Solution:

X=30

The second question:

70x( 1-4/7)x 1/6=5 people.

The third question:

50x( 1+0.6)=80 people.

The fourth question:

S=L (bottom circumference) xD (length) = 12.56x 100 (note here1m =100cm) =1256 (square centimeter).