If chargaff's equivalence rule is valid, then hypothetically we could extrapolate this to the combined genomes of all species on earth (as if there were one huge earth genome).

in other words, the total amount of a in every genome on earth should equal the total amount of t in every genome on earth.

likewise, the total amount of g in every genome on earth should equal the total amount of c in every genome on earth. calculate the average percentage for each base in your completed table.

do chargaff's equivalence rules still hold true when you consider those six species together?

yes . A approximately equals to T and G approximately equals C in average.

Explanation:

according  to Chargaff's equivalence rule

the number and concentration of adenine is similar to the number of thymine and number of guanine is similar to that of cytosine in the DNA.

so according to conditions given in the question i.e average amount of A should be equal to average amount of T and total average amount of G in every genome on Earth should equal the total average amount of C . so Chargaff's equivalence rules still hold true when you consider those six species together.  

i think the miocene epoch spans the time from 23 million to 12 million years ago.

its 42

i say its d?