Sue's Sushi placed two orders with its fish supplier. One order was for 15 pounds of salmon and 8 pounds of tuna; the order totaled $243. The other order was for 12 pounds of salmon and 6 pounds of tuna; this order totaled $192. What is the cost for one pound of salmon and one pound of tuna?

For this problem, make a system of equations.

15s+8t=243 | 12s+6t=192

Then multiply the second equation by 4/3 so you can have a common monomial to add/subtract out. You now have:

15s+8t=243 | 16s+8t=256

After subtracting, you have:

s=13

Now you can substitute s into one of the equations.

12 (13) + 6t=192

6t+156=192

6t=36

t=6

The final answer is that a pound of salmon is $13 and a pound of tuna is $6.