How do u make this word problem into a matrix? Please!! Thank you!!:)

Word Problem:The Nutty Food Company sells trail mixes and other snacks by the pound. A clerk is filling a barrel with peanuts, raisins, and carob-coated pretzels. The manager wants the associate to make 80 pounds of this mixture and to sell it for $3:35 per pound. The peanuts sell for $3.20 per pound, The raisins sell for $2.40 per pound and the carob-coated pretzels sell for $4.00 per pound.If the mixture has twice as many pounds of carob-coated pretzels as raisins, how many pounds of each ingredient should the clerk?
It would be very helpful if you could just set it up for me and I can do the rest.

I'm not sure where the matrix comes into play, but I'd solve it like this:

CC = carob coated pretzels
PP = peanuts
RR = raisins

You know there are twice as much CC as RR.
So lets already take 2 pound CC and 1 pound RR.
The price will already be 2*4 + 1*2.4 = $10.4 per 3 pounds

Now we need to add x pounds of PP so that the price will end up being $3.35 per pound

When you add x pounds of PP, the total price will be 10.4 + x * 3.2
The total weight will be 3 + x
So the price per pound will be (10.4 + x * 3.2) / (3 + x)
And that must equal 3.35
so
(10.4 + x * 3.2) / (3 + x) = 3.35
10.4 + 3.2x = 3.35 * (x + 3)
10.4 + 3.2x = 3.35x + 10.05
3.2x - 3.35x = 10.05 - 10.4
-0.15x = -0.35
x = 0.35 / 0.15
x = 7/3

For each 2 pounds of CC and 1 pound of RR, he needs to add 7/3 pounds of PP.
That will make a total of 1 + 2 + 7/3 = 16/3 pounds

You need 80 pounds, so you need to multiply each ingredient by
80 / (16/3) = (80 * 3) / 16 = 240 / 16 = 15

2 * 15 = 30 pounds CC
1 * 15 = 15 pounds RR
7/3 * 15 = 35 pounds PP

total : 30 + 15 + 35 = 80 pound

the price:

(30 * 4 + 15 * 2.4 + 35 * 3.2) / 80 =
(120 + 36 + 112) / 80 =
268 / 80 =
$3.35 per pound