Thouse events are independent, so we can calculate them separately and the final rpobability will be the product of them.
[tex]P(A\, and\, B)=P(A)\cdot P(B)[/tex]The first event, say A, is of landing on gray. Since 7 out of the 10 are gray, the probability is:
[tex]P(A)=\frac{7}{10}[/tex]Th second event, B, is of landing on blue. Since 3 out of the 10 are blue, the probability is:
[tex]P(B)=\frac{3}{10}[/tex]So, the probability of both is:
[tex]P(A\, and\, B)=P(A)\cdot P(B)=\frac{7}{10}\cdot\frac{3}{10}=\frac{21}{100}[/tex]