HELP!!!!!!!!!!!!!!

Prospectors are drilling for oil. The cost of drilling to a depth of 50m is £500. To drill a further 50m costs £640 and hence the total cost of drilling to a depth of 100m is £1140. Each subsequent extra depth of 500m costs £140 more to drill than the previous 50m.
a) Show that the cost of drilling to a depth of 500m is £11300.
b) the total sum of money available for drilling is £76000. Find, to the nearest 50m, the greatest depth that can be drilled.

What seems to be the problem so you ask for help with 12 exclamation marks ...

I don't know where to start. I'm sooo confused

ok what topic do you think is involved here?

Arithmetic series

Think about it. It goes up 140 quid every 50M extra. The first 50M = 500 quid, from 50-100 it is 640.. so from 100 to 150 it will be 780... 150 to 200 will be 920... continue that up to 450-500 which is 1760. Add all of the totals, you get 11300.

Think about it. It goes up 140 quid every 50M extra. The first 50M = 500 quid, from 50-100 it is 640.. so from 100 to 150 it will be 780... 150 to 200 will be 920... continue that up to 450-500 which is 1760. Add all of the totals, you get 11300.

very good
they are saying

first 50 m .......total depth 50m ........... £500
next 50m ........total depth 100m ..........£(500 +140)
next 50m ........total depth 150m...........£(500 +140 x 2)
next 50m ........total depth 200m...........£(500 +140 x 3)


form an arithmetic progression by identifying the first term and common difference and use the standard formulas

Thanks.