Answer:
b. Invalid, because the sample may not be representative of the population.
Step-by-step explanation:
A sample of around 10% of the population is needed to be representative.
In this question:
We have a population of 500,000, and a sample of 10,000.
10,000/500,000 = 1/50 = 0.02 = 2% of the population, so not representative, and option b is correct.
b must be equal to -6 for infinitely many solutions for system of equations
and 
<u>Solution:
</u>
Need to calculate value of b so that given system of equations have an infinite number of solutions

Let us bring the equations in same form for sake of simplicity in comparison

Now we have two equations

Let us first see what is requirement for system of equations have an infinite number of solutions
If
and
are two equation
then the given system of equation has no infinitely many solutions.
In our case,

As for infinitely many solutions 

Hence b must be equal to -6 for infinitely many solutions for system of equations
and
Answer: 
Step-by-step explanation:
The equation of the line in Slope-Intercept form is:

Where "m" is the slope and "b" is the y-intercept.
You need to find slope of the line with the formula:

Pick to points of the given line. You can choose the point (60,3) and the point (30,2).
Then, substituting into the formula:

You can observe in the graph that the line intercepts the y-axis at the point (0,1), therefore "b" is:

Substituting the slope and the y-intercept found into
, you get the equation of this line:

Where "y" represents the Height (1,000 ft) and "x" represents the Time in seconds.