The amount to be spent is A=$8400.
The contribution from the parents is 40% which is equivalent to,
[tex]8400\times\frac{40}{100}=3360[/tex]The remaining amount is,
[tex]8400-3360=5040[/tex]The amount to be saved per month can be determined as,
[tex]\frac{5040}{4\times12}=105[/tex]Thus, Lexi needs to save $105 per month for her first year of college.