Math problem...?

Question

"Cost $0.79 a pound, cashews $2.49 and pound, and walnuts $1.89 a pound. A store clerk needs to make 2 pounds of mixed nuts using these three types so the total cost is $2.97. If she wants to use 3 times as much peanuts as cashews, find how much of each type of nut she should use?"

Answer 1

Peanuts = 0.79
Cashews = 2.49
walnuts = 1.89

Cost:
p(0.79) + c(2.49) + w(1.89) = 2.97

We also know:
p + c + w = 2 pounds
p = 3c

So, plug those into the cost formula:
(3c)(0.79) + c(2.49) + w(1.89) = 2.97
(2.37)c + (2.49)c + (1.89)w = 2.97
4.86c + 1.89w = 2.97

we can also make this equation into just c and w:
p + c + w = 2
3c + c + w = 2
4c + w = 2

Now you have two equations and two unknowns:
#1: 4.86c + 1.89w = 2.97
#2: 4c + w = 2

Solve #2 for w
w = 2 - 4c

Put that into #1 and find c
4.86c + 1.89(2 - 4c) = 2.97
4.86c + 3.78 - 7.56c = 2.97
-2.70c = -0.81
c = 0.3

Now go back to the previous equation
w = 2 - 4c
w = 2 - 4(0.3) = 0.8

Now...
p = 3c = 3(0.3) = 0.9

So....
peanuts = 0.9 lbs
walnuts = 0.8 lbs
cashews = 0.3 lbs

Answer 2

x = amount of cashews.
3x = amount of peanuts
So 2-4x = amount of walnuts
2.49x+3x(.79)+(2-4x)(1.89) = 2.97
2.49x + 2.37x + 3.78 -7.56x =2.97
-2.7x = -.81
x = .3 pounds of cashews
3x = .9 pounds of peanuts
2-4x = .8 pounds of walnuts