Explanations and assumptions: $6$ worksheets, each pertaining to accounts receivableoutstanding at each year$-$end. Worksheets Dec $312013,$ Dec $312014,$ Dec $312015,$ Dec$312016,$ and Dec $312017$ contain the historical data, and worksheet Dec $312018$ contains the outstanding receivables for which you need to estimate the allowance. There are five columns of data in eachworksheet: Column A presents customer I, Column B presents the total amount invoiced during the year, Column C presents the amounts outstanding at year end, Column D presents the date the outstanding invoice was issued, Column E presents the date the invoice was paid the following year $($this column is N$/$A inthe Dec $312018$worksheet.$)$ The firm had a different number of customers each year as well as total receivable sales. Assume that if the receivable was not paid over the course of the following year, the entireamount is written off. In that case, the corresponding cell in column D remains blank.Assume $4$ categories of aging receivables: $(1)0-30$ days outstanding, $(2)30-60$ days outstanding,$(3)60-90$ days outstanding, and $(4)$ over $90$ days outstanding. Analysis: a$.$ For each year, calculate the percentage of accounts written off out of total sales on account. b$.$ For each year, calculate the percent written off in each outstanding receivable age $($think about which dates are relevant when aging receivables$).$

Can you give me an example and what the excel formula should use, based in the colums given. I need the excel formula for A question and B question. Repeat: the excel formula, considering I can't add any more columns.