6. At the end of year 5, an investment has grown to $750. This investment has earned annual effective rates of interest equal to i, = 0.0075n -0.0015 since issue. What was the size of the initial investment made at time 0? 7. How many days will it take a) $1,000 to accumulate to at least $1,200 at 5.5% simple interest, b) $1,600 to earn at least $30 of interest at 3.5%simple interest, and c) $5,000 to accumulate to at least $5,100 at 9% simple interest