(1) Amy needs to grill four steaks for her party
There is no information provided on when the guests will arrive. It will take Amy at best between 6 mins/steak * 4 steaks = 24 mins and at worst 7 mins/steak * 4 steaks = 28 mins to grill the steaks; if her guests arrive in 20 mins, the answer is no; however, if her guests arrive in 30 mins, the answer is yes; INSUFFICIENT.
(2) Amy’s guests will arrive in half an hour
There is no information provided on how many steaks need to be grilled. If Amy needs to grill 2 steaks, it would take her at best between 6 mins/steak * 2 steaks = 12 mins and at worst 7 mins/steak * 2 steaks = 14 mins; the answer is yes. However, if she has to grill 6 steaks, it would take her at best between 6 mins/steak * 6 steaks = 36 mins and at worst 7 mins/steak * 6 steaks = 42 mins; the answer is no; INSUFFICIENT.
Combined: SUFFICIENT; we know that Amy needs to grill 4 steaks and that her guests will arrive in half an hour. At best, it would take her 6 mins/steak * 4 steaks = 24 mins, and at worst, 7 mins/steak * 4 steaks = 28 mins. Therefore, she will finish grilling all the steaks before her guests arrive in 30 mins.
Answer is C.