Solution:

Make sure one of them is matchstick. :-)

Solution:

15/4 hours

Explanation:
Let us say they drive for "t" hours and initial fuel is "f"
Amount of fuel consumed by Fernando car is ft/4
Amount of fuel consumed by Sebastian car is ft/5

As per given condition,
f - ft/5 = 4(f-ft/4)
t = 15/4 hours

Solution:

The farmer will be able to sell 0 oranges because the tree gives mango, not oranges.

Solution:

927

Explanation
1) 5 4 7 : 7 is placed correctly
2) 5 3 0 : None of the numbers is in the code
3) 2 5 9 : 2 & 9 are correct number of code but placed at wrong position
4) 7 0 6: Number 7 is there but placed at wrong position
5) 6 4 9: Number 9 is there but placed at wrong position

Solution:

Initially, there are only two apples on the tree. I got one apple using the slingshot and therefore now one apple is on a tree and one with me.

Note: We got one apple(not apples).

Solution:

A pair of shoes

Solution:

It is an hourglass.

Solution:

The dead guy is Superman. He died because he was exposed to a Kryptonian rock.

Solution:

She is just trying to make up her mind. :-)

Solution:

Amin is the terrorist

Explanation:
The message is "tstimeirorwatchretehourhtsisecondsnidialma"

Step1 :
Rewrite the above message as
"ts time iror watch rete hour htsi seconds ni dial m"

Step2:
Now remove all words related to time like (time,watch,hour,seconds,dial) and combine them.
"tsirorretehtsinima"

Step3
Reverse the word.
"tsirorretehtsinima"

Step4.
Add spaces where necessary
"tsirorret eht si nima"

Step5:
Reverse again
"amin is the terrorist"