how to consistenly get 120++ CS at 10 minutes as safelane carry?

pro player always get that 120 cs at 10minutes

at my games legend 4 the supports is passive as fuck not even blocking heavy camp not harrass and zoning enemy

I have buy the sentry by myself at minute 0 and always doing it

but the lane is always hard 1vs3

I'm thinking about tp offlane at minute 10 but the offlaner is just tp bottom to farm passively with his dagger

EDIT: actually its not 10 minutes but 15

at 10 minutes usually they got 60

SO how many last hit at 10 and 15 mark to be considered as good?