The :filter prefix is the major piece you were missing: it lets us reject all the [tag[current]Y[1]] titles that don’t have a “week” value > 7 without modifying the input titles the way get normally does. This allows us to use get[£] in the next step.
The :reduce filter run prefix lets us do in one step what the combination of :map[get[£]] +[sum[]] does in two. First, for each input title, get the value of the “£” field. Then add up all these results.