can anyone help me with a couple question's about rate of change?

Question

anonymous · Answer

Cathy lives in a state where speeders are fined $11 for each mile per hour over the speed limit. Cathy was given a ticket for $99 for speeding on a road where the speed limit is 65 miles per hour. How fast was Cathy driving?

71 mph
79 mph
74 mph
78 mph

zepdrix · Answer

Let x be the number of "speeding" miles Cathy is going.

11x   <-- this is 11$ for each "speeding" mile.

So if Cathy was given a $99 ticket, we could write an equation like this:
11x=99
$11 per mile equals 99 total dollars.
Then let's solve for x!

Hmm if the speed limit is 65, we our final step will be to add x to 65.

anonymous · Answer

@zepdrix what's x

anonymous · Answer

74 mph got it.

zepdrix · Answer

Yay gj \c:/

anonymous · Answer

Forrest Lumber purchased a table saw for $810. After 2 years the saw had a depreciated value of $630. What is the amount of yearly depreciation?
@zepdrix  can you help me with this?

$90
$75
$180
$105