Ella has some pieces of milk candy and fruit candy in a box. At first, the ratio of milk candy to fruit candy was $$7:9$$. After Ella ate eight pieces of milk ones, the ratio changed to $$2:3$$. How many pieces of milk candy were there in the beginning? 
Overseas Competition->Knowledge Point->Word Problem Modules->Solving Problems Involving Proportions->Ratio Word Problems with an Invariant Part