Answer:
2.77777778
2/3 cubed is 0.222222222 and 3-2/3^2 is 2.77777778
It should be k= 4 or -1/3
Use the formula below.
Let A_0 = 1 because you just want to know the percentage left. Usually that's the initial amount.
t = 15, the number of years past. n = 22, the half-life.
2.5/2 = 1.25 litres per kilo
1.25 * 50 = 62.5 litres
Solution: 62.5 litres of fuel