Sets

If $$A = \left \{1, 2, 3, 4\right \}$$, what is the number of subsets of A with at least three elements?
Which of the following is equivalent set
(i) $$A=\{2,3,5,7\}$$
(ii) $$B=\{a,e,i,o,u\}$$
(iii) $$C=\{-1,-9,-8,-7\}$$
Which of the following is set
Find the smallest set $$\displaystyle Y$$ such that $$\displaystyle Y\cup \left \{ 1, 2 \right \}=\left \{ 1, 2, 3, 5, 9 \right \}$$
If $$G = \{7, 8\}$$ and $$H = \{5, 4, 2\}$$, find $$\displaystyle G\times H $$ and $$\displaystyle H\times G $$.