Let x represent the number of shirts. Let y represent the number of pens.
If shirts are on sale for $11.99 each, then x shirts cost $11.99x.
If pants are on sale for $12.99 each, then y pants cost $12.99y.
The total cost is $(11.99x+12.99y).
Sarah can spend up to $65. Then an inequality that represents this situation is
11.99x+12.99y≤65 (this inequality holds when Sarah can spend $65 too)
or
11.99x+12.99y<65 (this inequality holds when Sarah can spend less than $65).
