Well, my Japanese is very basic so I've tried to break it down into seperate Romanji for us to understand. From what I can tell its:
"Wa, imagoro nani suteru ka naa"
Which, literally speaking is:
"Concerning this subject (wa), at this time (imagoro) what (nani) abandon/give up (suteru) I wonder (ka naa)."
Also, remember that Yoshino doesn't REALLY know Makoto is Mako-chan (possibly), so she is talking about her in absence. Combine that with the segmented translation above, then put it into context and we get sooooooomething along the lines of:
"I wonder if Mako-chan has given up (on completing the homework) by now?"
I'm probably very wrong, but theres no harm in trying.