[Question]: Two brick walls are being built. Each wall has 30 bricks in a single row and there are 50 rows in each wall. How many bricks will be used to make both walls?
[Answer]: Each brick wall needs 30 x 50 = 1500 bricks. Thus, the two walls need 1500 x 2 = 3000 bricks.
So the answer is 3000.

[Question]: The number of short students in a class is 2/5 of the total number of students. If there are 90 tall students, and the class has 400 students, calculate the total number of students with average height.
[Answer]: The number of short students in the class is 2 / 5 * 400 = 160. The total number of short and tall students is 160 + 90 = 250. Since there are 400 students in the class, the number of students with average height is 400 - 250 = 150.
So the answer is 150.

[Question]: Alani earned $45 for 3 hours of baby-sitting. At the same rate, for how many hours would she need to baby-sit to earn $75?
[Answer]:
The rate is $45 / 3 = $15 / hr. She would need to baby - sit for $75 / $15 = 5 hours.
So the answer is 5.