線性代數vector spaces的問題！求救！?

Let v1=(1,0,1),v2=(2,1,3),v3=(4,2,6), and w=(3,1,2).
a. Is w in {v1, v2, v3}? How many vectors are in {v1, v2, v3}?
b. How many vectors are in Span{v1, v2, v3}?
c. Is w in the subspace spanned by {v1, v2, v3}? Why?
請問這問題該怎麼解
解答上說明是
a.There are only three vectors in {v1, v2, v3}, and w is not one of them.
b. There are infinitely many vectors in Span{v1, v2, v3}.
c. w is in Span {v1, v2, v3}.
但是小弟我實在是看不懂
請教各位數學高手ˊˋ