where my math freaks at.... have my TEN points!!!?

[4u2nv]

1. A system of five equations in the unknowns x, y, z, u and v, has a unique solution which is a permutation of the numbers 1, 2, 3, 4 and 5. Five students in an exam were asked to solve this system, but they were only able to provide the following partial answers before the end of the alloted time:
Jay: z = 1, u = 2 Bob: y = 3, v = 2 Zalik: z =5, u = 3 Dave: x = 4, v = 2 Zhuri: x = 4, y = 1.
In their partial answer above, each of the student had found the correct value of exactly one unknown. What is the value of v + x + z?
a. 6 b. 7 c. 8 d. 9 e. 10

2. Suppose a and b are positive integers such that (a + 2b) (a - b) = 10. What is the value of 2a - b?
a. 1 b. 3 c. 4 d. 5 e. 7

3. Zhuri buys apples at three for $1. She resells them at five for $2. Assuming that she resells every apple that she buys, how many apples must Zhuri buy in order to make a profit of $10?
a. 75 b. 150 c. 225 d. 300 e. 375