Answer: 4.25 Km
Explanation:
First you're going to consider the first number given as the main one to start with. (1.5 km)
The question told you that the hiker first went north so you can consider north positive, then he walked back south 0.45 km.
So far your calculation should be 1.5 - 0.45 = 1.05
Then the hiker walks again north with a distance of 3.2 km
so now add that to your value (1.05) as 1.5 and 3.2 are going to the same direction and 0.45 is only opposing them
Final calculation: 1.05 + 3.2 = 4.25 (1.5 - 0.45 + 3.2)
Another way of explaination if you didn't get this one:
The two values 1.5 and 3.2 are mentioned to be in the same direction (north), while 0.45 is mentioned to be opposing them going south, so you can either consider it as
(+)1.5 + 3.2 - 0.45 (But this one would make more sense)
Or
- 1.5 - 3.2 + 0.45
Hope you understood and good luck with your studies :D