Time for a Lump Sum to Double

To the closest year, how long will it take $$200$ to double if it is deposited and earns the following rates? $[$Notes: $(1)$ If you are using a financial calculator, you can enter the known values and then press the appropriate key to find the unknown variable. Then, without clearing the TVM register, you can $$override$$ the variable that changes by simply entering a new value for it and then pressing the key for the unknown variable to obtain the second answer. This procedure can be used in many situations, to see how changes in input variables affect the output variable. $(2)$ This problem cannot be solved exactly with some financial calculators. For example, if you enter PV $=-200,$ PMT $=0,$ FV $=400,$ and I $=7$ in an HP$-12$C and then press the N key, you will get $11$ years. The correct answer is $10\mathrm{.}2448$ years, which rounds to $10,$ but the calculator rounds up$.$ However, the HP$10$BII gives the exact answer.$]$ Do not round intermediate calculations. Round your answers to the nearest whole number.

$8\%.$

year$($s$)$

$12\%.$

year$($s$)$

$21\%.$

year$($s$)$

$100\%.$

year$($s$)$