Help Please Determine the lowest common denominator for each sum or difference.

Common Denominator: 10
Common Denominator: 12
Common Denominator: 24

13/24+7/12
7/6+(-5/12)
5-7/10
1/8-5/3
3/2-4/5

Trent wants to buy 2 packs of trading cards for 3 dollars each. the trading card packs that trent normally buys tend to come in packs of 6, 10, 12, or 15 cards. after selecting 2 packs, trent found that the first pack of cards cost 25 cents per card, and the second pack cost 30 cents per card. trent uses this information to write the equations below in order to compare c, the number of cards in each pack.

[10 points, algebra 2-simplifying complex fractions]according to my answer key the restrictions are -1 and 4. but why not positive 1?

Y+ 2/y is it a polynomial in one variable or not? and if so, why?