They ran a total of 9.5 km but Sandy ran 2.5 km more than Marisa.
so to see how much Marisa ran we can subtract the extra 2.5 from 9.5 that Sandy ran
We get 7 then we divide it into two (since there were two people)
that is 3.5
to find Sandy's run, add 2.5 to 3.5
Sandy ran 6 km and Marisa ran 3.5.
They ran that much in 30 mins.
To check:
add 6 to 3.5
that is 9.5
Hope this helps :)