What number should come in place of the question mark below?

Before the start of the car race, John and Jacob have the same amount of fuel in their car. With this fuel, John can drive for 4 hours while Jacob can drive five hours.
After a time they realize that the amount of fuel left in John's car is 1/4th of the fuel in Jacob's.

For how long they are racing?

Three cars are driving on a track that forms a perfect circle and is wide enough that multiple cars can pass anytime. The car that is leading in the race right now is driving at 55 MPH and the car that is trailing at the last is going at 45 MPH. The car that is in the middle is somewhere between these two speeds.
Right now, you can assume that there is a distance of x miles between the leading car and the middle car and x miles between the middle car and the last car and also, x is not equal to 0 or 1.
The cars maintain their speed till the leading car catches up with the last car and then every car stops. In this scenario, do you think of any point when the distance between any two pairs will again be x miles i.e. the pairs will be x distance apart at the same time ?

Make a sentence consisting of three words that have the whole alphabet.

Which country gets ill every time?

What does it mean?

Christina has four daughters, and each of her daughters has a brother. How many children does Christina have?

Solve the puzzle by telling what does below picture means.

Can you count the number of seconds in a year?

Clue: You need to bother about calculation.

My friends called me Iron59 because my parents are a chemist and a mathematician. What is my real name?