How could you determine what percentage of a strawberry's mass is dna?

Weigh the strawberry and record its total weight. Cut off a small piece of the strawberry, weigh the piece, and record the piece's weight. Crush the weighed piece and treat it with a substrate that will suspend particles with negative charges. Filter the materials suspended in the substrate to isolate the strands of DNA. Use imaging tools to find the exact mass of the DNA. Divide that mass by the mass of the strawberry piece and multiply by 100% to get the percentage of the strawberry's mass that is DNA.

First you determine the total mass of the strawberries used

Then determine the mass of the DNA obtained from the strawberries

percentage mass is therefore equal to mass of the DNA obtained divided by total mass strawberries multipy by a 100