Work out the area

This task is about using the diameters of tins to work out the floor area of a carton and a given number of tins.
a)


 

  Four paint tins each 12.5 cm in diameter, fit into a carton as shown. What is the area of the bottom of the carton?
 
  (A)
(B)
(C)
(D)
(E)
50 cm²
100 cm²
625 cm²
1250 cm²
None of these. The answer is __________ cm².
 
b)


 

  The 6 smaller paint tins packed in this carton each have a radius of 5 cm.
What is the total area of the bottom of all 6 paint cans? (Use = 3.14)
 
  (A)
(B)
(C)
(D)
(E)
78.5 cm²
188.4 cm²
471 cm²
600 cm²
None of these. The answer is _________ cm².