From a rough estimation of Marks VS rank

Marks --Rank

>190— —1

>140— —<50

>120— —<350

>100— —<1000

>90— —<1500

>80— —<2000

>70— —<3000

>60— —<5000

>50— —<8000

>40— —<10,000

>30— —<15,000

>20— —<20,000

>10— —<35,000

>5— —<50,000

Generally  a difference of 20 marks can boost your rank by 5000 or 6000 .In other words ,Rank increases exponentially with marks.

So with 100 marks in WBJEE 2018 you will most probably get a three digit rank.

For WBJEE Engineering Rank Vs Mark:-

185 Marks = 1 to 20 ranks.

180 Marks = 20 to 80 ranks.

175 Marks = 80 to 130 ranks.

170 Marks = 130 to 200 ranks.

130 to 100= 201 to 500 ranks.

All the very best and good luck.

Hii..

According to me,your expected rank will be around 900-1000.

Thanks..!!