If 100 cats killed 100 mice in 100 days, you can say that each cat killed one mouse the day after the last cat. So, if four cats killed four mice, and we're going of off the same basis that each cat killed one mouse the day after the last cat, then the answer would be 4.
The slope-intercept form:

m - slope
b - y-intercept
The formula of a slope:

We have two points (2, 0) and (-2, -4). Substitute:

Therefore we have the equation of a line

Put the coordinates of the point (2, 0) to the equation:
<em>subtract 2 from both sides</em>

Answer: 
you're absolutely correct.
each system is sold for $2150, that includes cost + markup, namely the markup is the surplus amount otherwise called "profit".
they sold 12 of those, 2150 * 12 = 25800
they had $4824.36 in profits from it, so if we subtract that from the sale price, we'll be left with the cost of all 12 systems
25800 - 4824.36 = 20975.64
that's the cost for all 12 systems sold, how many times does 12 go into 20975.64? 20975.64 ÷ 12 = 1747.97.
The probability that student scored more than 850 we shall proceed as follows:
z=(x-μ)/σ
where:
x=850
μ=750
σ=50
thus
z=(850-750)/50
z=2
thus
P(x>850)=1-P(x<850)=1-P(z<2)=1-0.9772=0.0228
Answer: P(x>850)=0.0228