Ok, first one:

To make it simple, a car dealership sells 12 cars one week and then 19 the next week. What is the percentage increase in sales from one week to the next?


Next question is:

If r= 5 z then 15 z = 3 y, then r =

I am confused by this so if someone can help me I would appreciate it.

Here is another one that is kind of similar to the first one:

If a dealer sells a car for $39,000, which represents 25% profit over the cost. What was the cost to the dealer? I know the answer to this but I don't know how to get to it.

Anyone have any solutions please?

Ok, #2 is in terms of y right?
So
r=5z
15z=3y
since 15/5=3 you can substitute 15z for 3r, now
3r=3y
divide by 3
r=y
now #1
12 to 19
the difference is 7 so 7/12 is the answer or 58.3 repeating
now #3
the equation is (25% u is 1.25)
1.25x=39000
divide by 1.25
you can do this

Ok, that all made very good sense. Thank you very much. I was taking 19/12 at first which gave me 1.58 and I knew the .58 part was right and wasn't sure about the rest.