Please help solve this finance problem. Thanks a lot!

3. Jr2 we will use in class aud (The 72 Rule) With the help of the approximation In(l + r) r the value In(2) 0.69, show that the number of periods (e.g. years) n required for an investment 10% (per period) to double in value is n 72/(100 * r). Create au Excel at interest rate r spreadsheet to assess the sensitivity of this approximate formula to the value of the interest rate r. For what value of the interest rate r is the "72 Rule" formula closest to the 'true' n?