A 20 year old building has been depreciated to $420,000 in value it has been depreciated at 2.5% per year what was its original value

The one above is incorrect (no offense) because you have to add 2.5% of its value and then calculate 2.5% of its new value and add that. You add because the value after being depreciated for 20 years is 420,000

It would be 210,000 cause 2.5x20 = 50% so 420,000 x 50%