allow me another way...
we have 1/4 of a sol'' taken away and 3/4 of the sol' remains and lets say as three parts of 1/4 now each 1/4 of the solution has = 10 mg of sugar...
a new sol'' is put and the whole = the three 1/4's and the new 1/4 th all now have 16 mg of sugar... which means that the new 1/4th has 10mg and an extra 6 mg not only that it has more so that each of the three 1/4 ths of the old sol'' to get to have 16 mg of sugar
now putting it clear old 3>. 1/4 th's must have each an extra 6 mg of sugar that is 3*6=18
the new 1/4 th sol' should have another extra 6 mg + the 10 mg= 16
now added up it gets to 34...
I hope that was clear ... in acse of doubt let me know
also the two previous expalnations were fab''