X in less than or equal to 4.5. it is this because 32 is the least number of miles per gallon. 144/32=4.5.
Going by the formula, Half-Life = ln(.5) / k
Half-Life = .693147 / .1205
Half-Life = 5.75 days and rounded to nearest tenth,
Half-Life = 5.8 days
Recall that for
, we have

Replace
with
and we get

Lastly, multiply this by
, so that

!/5x1/5 =2/5
!/5 one possible of the total of 5
Multiply both