If there are n coins, then the smallest (minimum) amount of coins we need to flip is 1. The reason why is because the best case scenario would be flipping all heads except the last coin which is tails. This scenario is rare if n is large, but still possible.
(2x-3)(5x-1). I Think that is the answer.
Exponential functions are in the form

, where <em>a</em> is the initial value, <em>b</em> is the growth rate (percent increase) + 1, and <em>x</em> is the number of time periods. Our initial value is 100, and we're given the growth rate + 1 (tripling is the same as increasing by 200%; 200%=2.0; 2.0+1=3). Therefore our function is

.
Adam: 15 miles / 3 = 5Mi/Hr
Ben: 12 miles / 2 = 6Mi/Hr
Hope this helps!