Find The Next Number In The Sequence

30 10 15 13 0 16 -15 ?

What is the word or phrase below?
R | E | A | D

We have four gears with below features=> Both Gear A and D has 60 teeth=> Gear B has 40 teeth=> Gear C has 20 teeth=> Every two minutes, Gear B makes 25 full turns.What is the relative speed of Gear A and Gear B?

I am a type of vehicle that has two wheels and is powered by humans. What am I?
Hint 1: You can ride me for exercise.
Hint 2: I am environment-friendly.

You have two strings whose only known property is that when you light one end of either string it takes exactly one hour to burn. The rate at which the strings will burn is completely random and each string is different. How do you measure 45 minutes?

You need to move three matchsticks to form three squares. Can you do it?

Can you count the number of triangles in the given figure?

I am soft and cuddly that soothe your heart. But, If you pick my last name I am going to tear you all apart. Who am I?

Why do we preferably have round manhole covers and not square ones?

Can you move 2 matchsticks to form four equal sized squares.