Q1 Many approaches. You can calculate a = b x c and then calculate b x a. Or you can use the formula for the vector triple product: Vector Triple Product -- from Wolfram MathWorld (then you only have to calculate scalar products).

Q2 Get e = a - b and f = a - c. Now calculate e x f. Add d to the result.

Youshouldknow how to calculate a cross/vector product ....

Slightly off-topic but this thread is too good an opportunity to pass up:

Question: What do you get when you cross a mountain-climber with a mosquito?

Answer: Nothing - You can't cross a scaler with a vector.