Arthro is making 5 pounds of snack mix from raisins and almonds. the raisins cost $3 per pound, and the almonds cost $8 per pound. he wants the cost of the snack mix to be $6.50 per pound. how many pounds of each item should he use?

This is a system of equations problem.
Let r = pounds of raisins
and a = pounds of almonds
We know that r + a = 5. this is our first equation
The second one is more tricky, 3r + 8a = 6.5*5
Now solve:
r = 5 - a
3(5 - a) + 8a = 6.5*5
15 - 3a + 8a = 32.5
5a = 17.5
a = 3.5
r = 5 - 3.5
r = 1.5
He should use 3.5 pounds of almonds and 1.5 pound of raisins