<span>Cost 1 pack = x
3x + 10 = 5x
2x = 10
x = 5
1 pack cost $5
Hope this helped</span>
If x is the amount that Tanya paid for each item, then Tony's items would be x-2.25. So:
3x=4(x-2.25)
3x=4x-9
x=9
x-2.25=6.75
Tanya spent $9 on each item; Tony spent $6.75 on each of his items

The appropriate choice is ...
... D) 1.0×10⁻³ inch