Hi, and welcome!
The key to getting more and better answer lies in the FAQ: What's a reproducible example (`reprex`) and how do I do one?
For your problem, at a minimum it should look like
dat <- c(1000,1000,200,200,200,200,100,100,100,100,100,100,60,60,60,60,60,60,45,45,45,45,45,45,45,45,12,24,12,24,12,24,12,24,12,24,12,24,12,24,12,24,12,24,12,24,12,24,12,24)
Created on 2020-02-13 by the reprex package (v0.3.0)
and, ideally, what you have tried.
Also, if applicable, see FAQ: Homework Policy
So, to start you need the median.
med <- median(dat)
Next, you need to subset for all observations below the median (assuming that you don't be at or below the median).
lower <- dat[dat < med]
The sum is easy enough
tot <- sum(lower)
as is the number of observations
obs <- length * tot
And with that, the + operator will give you a final result.