To solve this problem you must apply the proccedure shown below:
1. You have that
varies jointly as
and
and inversely as the product of
and
. Therefore, you can write the following equation, where
is the constant of proportionality:

2. Now, you must solve for the constant of proportionality, as following:

3. Susbtiute values:


4. Substitute the value of the constant of proportionality into the equation:

The answer is: 
-3 • (5x + 2y = 7)
-15x - 6y = -21
-2x + 6y = 9
__________
-17x = -12
x = 12/17
5(12/17) + 2y = 7
2y = 7 - 60/17
2y = 3.47
y = 1.735
Answer:
15
Step-by-step explanation:
Red : Blue :
3 8
We have 40 blue marbles
Multiply 8 by what to get 40
40/8 =5
So we need to multiply by 5
Red : Blue :
3*5 8*5
15 40
There are 15 red marbles
Bro that's a lot, i don't know what the heck you are talking about.