This is the answer 9(-4-3) = -63
The first one would be C and the 2nd is A.
A, B and C working together will finish same piece of work in 10 days
A can do a piece of work in 20 days. That is A is doing the work at a rate of 1 / 20. Therefore
B = 1 / 30
C = 1 / 60
A, B and C working togehter their rate will be added together =
A + B + C = 1 / 20 + 1 / 30 + 1 / 60 = 1 / 10
so they can work together to finish same piece of work in 10 days
when a=4 and b=3,
3.14((4 x 2)+ (4 x 3)) = 3.14(8+12) = 3.14 x 20 = 62.8
* r^2