You can work for up to k consecutive days,

Up to k days or exactly k days?

Why

Work for days 1 to 3: 50 + 60 + 70 = 180
Take a break on day 4
Work for days 5 to 7: 80 + 90 + 100 = 270
Last day: 20
Total earnings = 180 + 270 + 20 = 470

and not

Work for days 1 to 3: 50 + 60 + 70 = 180  
Take a break on day 4  
Work for days 5 to 7: 80 + 90 + 100 = 270  
Take a break on day 8 (last day)          <-------
Total earnings = 180 + 270 = 450          <-------