13. 68
14. y = 0.50x + 8
15. y = 25x - 15
16. y = 7x - 1
17. 
Step-by-step explanation:
13. f(3) means plug in 3 for x.
f(3) = 7(3)² + 5 = 7(9) + 5 = 63 + 5 = 68
14. Write out what you know. 0.50 inches per hour is the rate of snowfall, or your m, or your slope. m = 0.50. If x is hours passed and y is inches of snowfall, then you also know that at x = 4, y is 10. Plug these into the standard linear formula: y = mx + b => 10 = 0.50(4) + b
Solve for b:
10 = 0.50(4) + b
10 = 2 + b
b = 8
Remember, x and y are variables, not constants, but m and b are always the same for some given function. So your answer is y = 0.50x + 8
15. Write out what you know. If x is hours passed and y is distance from home in miles, then we need to find the slope and y-intercept using what you're given. How do you find the slope? Use this: 
.
You have two points given: (3, 60) and (7, 160). So 
Now, just use either of these points to find b, or your y-intercept.
y = mx + b
Let's just use (3, 60); either one would work though.
60 = 75 + b
b = -15
To make the equation, use the values for m and b that you found.
m = 25 and b = -15, so y = 25x - 15
16. In y = mx + b, b is the y-intercept, but it's also how much the graph shifts up or down from its "original" position. I don't really want to explain this, but you can experiment with y = x + something (like try y = x + 1, y = x - 1, y = x, y = x + 3) and you'll see the pattern of what I'm talking about. To move y = 7x + 3 down 4 units, just subtract 4 from 3 to get -1: you will get y = 7x - 1.
17. sorry I hope someone else gives u an explanation I'm kind of bored with these
