The mass per unit area of a disc is changing as (x + 2)/π kg/m^2 where x is the distance from the centre. If radius of the disc is 4m then:

A)mass of disc is 224/3 kg

B)mass of disc is 122π/3 kg

C)mass per unit area at centre is 2/π kg/m^2

D)mass per unit area is zero at the centre

More than one answers are correct. Please explain how to solve these types of questions too.