If the median of the following frequency distribution is 46, find the missing frequencies.

Variable: 1020 2030 3040 40---50 5060 60---70 70---80 Total

Frequency: 12 30 a 65 b 25 18 229

a) a = 32 b =40

b) a =31 b = 45

c) a = 33 b = 42

d) a =34 b =45