Jane is making a healthy snack of trail mix to sell as part of a fundraiser for the school hiking club. the mixture will have 2.5 times as many kilograms of raisins as of sunflower seeds. sunflower seeds cost $12/kg and raisins cost $6/kg. if jane has $108 dollars to spend, what mass of sunflower seeds and of raisins should she buy?
i have one formula, which is 12s + 6r = 108 but i need one more equation, plus how to solve it.

So the other equation is
2.5 times as many kilos of rasins than sunflower seeds or
rasin kilos=2.5 times sunflower seed kilos
r=2.5s

the 2 equations are
12s+6r=108 and
r=2.5s
you can simplify the first equation (that sometimes helps)
undistribute the 6 from both left side
6(2s+r)=108
divide both sides by 6
2s+r=18

now use r=2.5s and subsitute 2.5s for r in first equation
2s+2.5s=18
4.5s=18
divide both sides by 4.5
s=4
subsitute
r=2.5 times s
s=4
r=2.5 times 4
r=10

rasins=10 kilos
sunflower seeds=4 kilos