What was the total yield of dna from the plasmid prep

A student performed a BioRad miniprep of plasmid DNA that resulted in 100ul(microliter) of DNA solution. To determine the concentration of this solution, 20ul of the DNA solution was placed in 480ul of water and the absorbance of the diluted sample was measured at 260nm. The absorbance relative to a blank was 0.225

a. What was the total yield of DNA from the plasmid prep? Recall that the molar extinction coefficient of DNA at 260nm is 20cm^2/mg, so 1.0 Absorbance unit=50ug/ml.

b. If the student needs 4ug(micrograms) for a transformation, what volume of the plasmid prep should he use?

"Is this question part of your assignment? We can help"