78 since pattern becomes add multiple of 6 increasing every two additions. 4 seems to be an outlier however. After 4 add 6 to 6, add 6 to 12 then add 12 to 18 then 12 to 30, add 18 to 42 then 18 to 60 to get 78. Finally 102 comes from adding 24 to 78.