How many tens must be added to $$215$$ to make $$985$$?~\uline{~~~~~~~~~~}~tens 
Overseas Competition->Knowledge Point->Word Problem Modules->Solving Problems Involving Proportions->Ratio Word Problems with Invariant Sums Overseas In-curriculum->Knowledge Point->Operations of Numbers ->Addition and Subtraction of Whole Numbers->Adding and Subtracting within 10000->Subtraction of 3-digit Numbers
$$985-215=770$$  $$770\div 10=77$$ 