How do you work this out?

Answer:
£365
Step-by-step explanation:
so add another column and call it midpoint. use the weekly earnings column to find the midpoints add both numbers then divide by 2
then times all these numbers by the corresponding frequencies
1 * 200=200
11 * 300=3300
5 * 400=2000
0 * 500=0
3 * 600=1800
then add these numbers =7300 then do 7300/20=365