for teh second question,

 

there is a possibility of getting either 1 or 2 or 3 and so on upto6 for one die, and similarly for the other three dice. So for finding the sum as 8, u need to find the coefficient of x⁸ in (x¹+x²+x³+x⁴+x⁵+x⁶)⁴ which on solving will give the answer.