The answer is 6 and 1/15.
The answer is; 24/75 of the entire cake remained
If 2/5 of the initial cake was eaten, the 3/5 is what remained
MInu ate 1/3 of the 3/5 = 3/15
3/5 – 3/15 = 6/15 remained
Her brother ate; 1/5 of 6/15 = 6/75
6/15 – 6/75 = 24/75 remained
Well... the segment FG = 4x + 3, the segment GH = 7x - 12, now, the
segment FH = FG + GH, those two fellows added up, and we know that FG and GH are both equal halves because G is the midpoint.
thus, FG = GH
or

and fairly sure, you know how much that is.
Lol that's so cool just give me the poonts