hi everyone!

I need help with these two problems. thanks in advance!

1. A 100-ft oil is to be drilled.The cost of drilling the first foot is $10.00, and the cost for drilling each additional foot is $.50 more thaan that of preceding foot.Find the cost of drilling the entire 100ft.

2.A tank contains 20 galloons of water.One half of the water is removed and replaced with antifreeze.This process is continued eight times.How much water remains in the tank after these eight replacements process?