Find The Next Number In The Sequence

30 10 15 13 0 16 -15 ?

A train leaves from point A for point B at 80 mph. After half an hour, another train leaves from point B for point A at 60 mph.

Which of the trains will be farther from point A when they meet ?

Move three sticks of the spiral below to form a square.

1 + 9 + 8 = ?
considering, 28 + 8 + 92 = 10

A boy was locked in a room by some robbers. All that is in the room is a piano, a calendar, and a bed. The room is locked from the outside. What does he eat, drink, and how does he escape and get out?

I am an odd number. Take away a letter and I become even. What number am I?

In four steps you need to move the word 'cold' From 'warm' by replacing one alphabet at a time such that every word formed at each step is acceptable in English Dictionary.

Replace the question mark with the number below given a simple math problem.

There is a jar in which there are two types of candies.
20 blueberries and 16 strawberries. You perform the following steps:
1) You take out two candies.
2) If the two candies are of the same flavour, you add a blueberry one otherwise, you add the strawberry one.

You repeat these two steps till there is just one candy remaining in the jar. Which flavoured candy will be left?

Can you find the next number in the below sequence
3 , 7 , 10 , 11 , 12 , 17 ?