In a certain candy store, 3 pounds of candy and 2 pounds of mints cost $10.80, and 1 pound of candy and 3 pounds of mints cost $5.35. what is the cost per pound of the mints?
mints are 65¢ per lb
mints are 75¢ per lb
mints are 85¢ per lb

 This is an application of linear equations in two variables 

Let c = candies(in pounds) ; m = mints(in pounds also) 

From this sentence >> 3 pounds of candy and 2 pounds of mints cost $10.80 

you can make-up an equation >> 3c + 2m = 10.80 right? 

That's your first equation, 3c + 2m = 10.80 ... (1) 

and from this sentence >> 1 pound of candy and 3 pounds of mints cost $5.35 

you can make-up an equation >> c + 3m = 5.35 ... (2) 

you can use various methods here, like graphing, substitution, comparison, and elimination method. 

Let's try using substitution method. 

3c + 2m = 10.80 ... (1) 
c + 3m = 5.35 ... (2) << here you can come up with c = 5.35 - 3m then substitute it to (1) 

3c + 2m = 10.80 ... (1) 
3(5.35 - 3m) + 2m = 10.80 
16.05 - 9m + 2m = 10.80 
-7m = -5.25 
m = 0.75 <<This is the price of the mint 

to get the price of candy, simply substitute m = 0.75 to (1) or (2) if you want, it depends on you. 

Either way, you will have the same answer. 

Let's try substituting in (1) 

3c + 2m = 10.80 ... (1) 

3c + 2(0.75) = 10.80 

3c + 1.5 = 10.80 

3c = 9.3 

c = 3.1 <<this is the price of the candy