How to do 3+6 i can't get it

Earth's atmosphere is unique among the planets and is able to support life because it contains a large amount of a) oxygen b) helium c) methane d) carbon dioxide

Abag contains even and odd numbered balls in the ratio of 3: 7, respectively. for each of the following, what is the probability of drawing an even-numbered ball? the total number of balls is 240 and 30 of the odd-numbered balls are renumbered by multiplying the numbers by 4.

Ineed so much with both of these tot