Answer: she bought 11 pounds of cashew nuts.
Explanation:
Let x represent the number of peanuts that she bought.
Let y represent the number if cashew nuts that she bought.
Elijah bought a total of 16 pounds of peanuts and cashew nuts. This means that
x + y = 16
If peanuts cost 2.75 dollars per pound, and cashew nuts cost 3.25 dollars per pound and she paid 49.50 for all she bought, it means that
2.75x + 3.25y = 49.5 - - - - - - - - - 1
Substituting x = 16 - y into equation 1, it becomes
2.75(16 - y) + 3.25y = 49.5
44 - 2.75y + 3.25y = 49.5
- 2.75y + 3.25y = 49.5 - 44
0.5y = 5.5
y = 5.5/0.5
y = 11
x = 16 - y = 16 - 11
x = 5