SAT questions I did not understand

Can someone give me an explanation for Q1? I am still confused.

Q1.

In a supermarket, Shakira bought 5 items from aisles 1 through 7, inclusive, and 7 items from aisles 4 through 10, inclusive. Which of the following could be the total number of items that Shakira bought?

I. 9

II. 10

III. 11

A. II only

B. I and II only

C. I and III only

D. II and III only

E. I, II, and III

A purchase from aisles 4 through 7, inclusive, would count in both Shakira’s purchases from aisles 1 through 7, inclusive, and those from aisles 4 through 10, inclusive. So, for example, she could have bought as few as 7 items total: say 5 items from aisle 6 and 2 from aisle 9. Or the total could be as high as 12: say 5 items from aisle 1 and 7 from aisle 10. Any total number of items between 7 and 12 is also possible. In particular, Shakira could have bought 9 items total (for example, 2 items from aisle 1, 3 from aisle 6, and 4 from aisle 10), 10 items total (for example, 3 items from aisle 1, 2 from aisle 6, and 5 from aisle 10), or 11 items total (for example, 4 items from aisle 1, 1 from aisle 6, and 6 from aisle 10). Therefore, the correct answer is I, II, and III.

(ANSWERED)

Q2. Maria is 6 times as old as Tina. In 20 years, Maria will be twice as old as Tina. How old is Maria now?

( I'm recalling this from memory. Correct me if you've seen a problem like this before and this one doesn't make sense.)

Q3. Let T be the sum of numbers 1 to 51 and let Q be the sym of numbers 51 - 100. What is Q-T?

(Same thing, I'm recalling this from memory. Correct me if i'm wrong.)

Q4.

At Central High School, the math club has 15 members and the chess club has 12 members. If a total of 13 students belong to only one of the two clubs, how many students belong to both clubs?