Question 1:
I believe there is a typo in the question. Stmt 2 should be $1.50 more. Now, moving onto the solution:

Lets say,
p = number of people who attended
a = admission fee per person in dollars

stmt 1: (a - 0.75)(p + 100) = pa ==> So, Insufficient to obtain p.
stmt 2: (a + 1.50)(p - 100) = pa ==> So, Insufficient to obtain p.

Stmt 1. and 2. together: SUFFICIENT to solve for p. It works out to 300 people.

Question 2:
Since, the question is relating to determining the point of intersection with the x-axis: y = 0.

So, (x + a)(x - b) = 0. This equation has two roots: x = -a and x = b.

stmt 1: a + b = -1 ==> Insufficient to determine a, b
stmt 2: substituting (0,-6) in the equation yields :

ab = 6. Insufficient to determine a, b.

But combining both a + b = -1 and ab = 6, we can get the values for a and b. So, stmt 1. and stmt 2. both put together can be solved for the points of intersection.

But the quadratic equations has no real roots.

Therefore, the function y = (x + a)(x - b) does not intersect the x axis.

Cheers,

Nand