The rule of 70 states that the doubling time or the time required to double an investment is equivalent to 70 divided by the interest rate. So in this case the interest rate is 7%, so the doubling period is:
doubling period = 70 / 7 = 10 years
Therefore the investment doubles every 10 years. So:
0 year = $100
10 year = $200
20 year = $400
30 year = $800
40 year = $1600
50 year = $3200
Answer:
$3200