Some Random Questions....

Hello! I'm having some difficulty with these questions. Thanks for the help!

1.

If a = 2j - 3k

b = 3i - 3j + ck

and

abs(a+b) = root35

Then c is equal?

2.

The angle between vectors a and b is 120 and abs of a = abs of b. The angle b/w a and a + b is?

3.

A woman of mass 50kg stands in a lift which is moving upwards with acceleration of am/s^2. THe floor of the lift exerts a force of magnitude 75g Newtons on the women. Then value of a is?

4.

A body of mass 15kg slides down a straight slide which is inclined at an angle of 30 degrees to horizontal. The normal force, in Newtons of the slide acting on the boy is?