We can find the acceleration via

We have


Then by definition of average acceleration,

so that


We alternatively could have found the time without knowing the acceleration. Since acceleration is constant, the average velocity is

Then


If the selling price is marked up by 25 percent, the new price will be $10.
8 * 1.25 = 10
If the selling price is marked up by 70 percent, the new price will be $13.60.
8 * 1.70 = 13.6
If the selling price is marked up by 75 percent, the new price will be $14.
8 * 1.75 = 14
The answer to this question is 71