Total cost of cashews + Total cost of peanuts = Total cost.
total cost of cashews=$7 * x=7x
total cost of peanuts=$3 * 9=27
total cost=(9+x) * $5=45+5x
7x+27=5x+45
subtract 5x from both sides:
2x+27=45
subtract 27 from both sides:
2x=18
x=9 pounds of cashews