Need help understanding half-life/decay problem for upcoming test.

Question

A water filter is constructed to form a foam that removes 25% of the particulate impurities for each inch of foam.

1.What percentage of the particulate impurities will be removed by a filter consisting of two inches of?
2. How many inches of foam are needed for the filter to remove 50% of the particulate impurities.

Can you explain in either the A=Pa^x or A=Pe^-rx form?

I just mainly need help on setting up the problem.

Thank You Very Much.

Answer 1

Please ignore this question. I was a able to get it.

Thanks For Reading!