The answer is: 2 years and 1 month. This duration at $100 per month totals to $2,500. The calculation is $720 per year over 2 years results in $1,440. Monthly, this amounts to $60, making the total $1,500 after adding the two figures. Therefore, $4,000 - $1,500 leaves us with $2,500.
The likelihood that 0≤x≤1/2 and 1/4≤y≤1/2 is calculated to be 3/64 (4.68%).