If you flip a fair coin 4 times, what is the probability that you will get exactly 2 tails?

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.

Can someone explain to me how to do

At your job you're paid $50 per week plus $3 per sale at least how many saled do you need to make in order to have over $250