需要帮助找出可重复的等于和添加操作员事件

I am building a UWP calculator app using the MVVM pattern and I have just about everything figured out except how to get the equals button to calculate repeatedly and have my operator buttons work correctly. I can do one or the other, but I can't figure out how to do both. The code below works for a repeatable equals button, but the plus operator will yield the wrong answer when adding multiple values.I am building a UWP calculator app using the MV