On a certain date, Pat invested $10,000 at x percent annual interest, compounded annually. If the total value of the investment plus interest at the end of 12 years will be $40,000, in how many years, the total value of the investment plus interest will increase to $80,000?  Options:
A) 15	B) 16	C) 18	D) 20	E) 24
x- interest rate   80.000= 10.000 (1+x)^year   =&gt; 8=(1+x)^year   40.000=10.000 . (1+x)^12   =&gt; 4= (1+x)^12   =&gt;2= (1+x)^6   =&gt; 8 = (1+x)^ 18   So, after 18 years, the total value of the investment plus interest will increase to $80,000.   ANSWER:18
<result>C</result>
On a certain date, Pat invested $10,000 at x percent annual interest, compounded annually. If the total value of the investment plus interest at the end of 12 years will be $40,000, in how many years, the total value of the investment plus interest will increase to $80,000?