This problem requires us to calculate, the value of investment after 10 and 25 years, and also tell the time after which intial investment amount will double. Investment rate and initial investment amount is given in the question.
Value of investment after 10 year = 600(1+8%)^10 = $ 1,295
Value of investment after 25 year = 600(1+8%)^25 = $ 4,109
We know that 50% of the number is 150 so we can assume the number is 300(if its 50% just double that number). Next we use the equation 0.80 x 300 which gives us the answer 240.