Gyou extracted your dna from cheek cells. the concentration of your dna sample is 250 ng/μl. the dna template for pcr should be 10 ng/μl. you should mix μl of your dna sample and μl of water to make final volume of 100 μl of dna that has the concentration of 10 ng/μl.

You should mix 4µl of DNA sample and complete it with 96µl (100-4) of water.

You can figure this out by using  C1.V1 = C2.V2
C1 = 250 ng/μl (Sample Concentration)
V1 = ?          (the necessary volume to take from the DNA sample)
C2 = 10 ng/μl (PCR concentration)
V2 = 100 µl (total volume)

V1 =  = = 4µl

For the water: 100µl (total volume) = 4µl + Water
Water volume = 96µl

Is this a question? i'm confused