[求助]另外一道PREP数学

以下是个表 （我不会画）

shipment       Number of defective chips in the shipment       Total number of chips in the shipment

S1                 2                                                                       5,000

s2                 5                                                                        12,000

S3                6                                                                         18,000

S4                4                                                                          16,000

A computer chip manufacturing expects the ratio of the number of defective chips to the total number of chips in all future shipments to equal to the corresponding ratio for shipments S1, S2, S3 and S4 combinded, as shown in the table above. What is the expected number of defective chips in a shipment of 60,000 chips?

A  14

B  20

C  22

D  24

E  25 

answer: 20