1) As a start you have 100% of contaminants: so
the 1st filtration you removed 70% & remaining 30%
the 2nd filtration you removed 70% of the 30% (=21%) & remaining (30%-21%)
or 9%
the 3rd filtration removed 70% of the 9% (=6.30%) & remaining (9%-6.3%)
or 2.7%
the 4th filtration removed 70% of the 2.7% (1.89%) & remaining (2.7%-1.89%)
or 0.81%
Follow the same logic for all remaining question.