Answer :
Answer:
30 pounds of $9 brand
10 pounds of $3 brand
Step-by-step explanation:
let x = $9 brand
let y = $3 brand
system of equations:
x + y = 40
9x + 3y = 40(7.5)
substitution method: x = 40 - y
9(40 - y) + 3y = 300
360 - 9y + 3y = 300
360 - 6y = 300
-6y = -60
y = 10
so, x = 40 - 10 or 30