"The cross section of a large circular conduit with radius 12.00 cm has seven smaller equal circular conduits within it."

a) calculate the shaded area ( its the area minus the seven smaller circles )

b) what fraction of the large conduit is occupied by the seven smaller conduits? - this seems to be like The entire circle area over the seven smaller ones

So how would i do part a) without the radius of the smaller circles?

** i apologize for posting twice once in pre calc forum and once here but i accidentally posted in that forum**