If you finished 3/4 of your journey, you have 1/4 of your journey left.
Your journey is x miles.
In words "3/4 of your journey is 16 km." In math:
3/4 * x = 16
Figure out what is x.
3/4 * x = 16
3x = 64
x = 64/3
So your total journey is 64/3.
You have 1/4 of your journey left.
1/4 * x = ?
1/4 * 64/3 = ?
16/3 = ?
You have 16/3 km left.