Please give me the correct answer

Abox of chocolates costs $7. which equation relates the number of boxes sold (x) and total cost of the boxes sold (y)?

Add, subtract, multiply, or divide as indicated. list any restrictions for the variable(s) and simplify the answers when possible. 1) x-2 / x+5 + 3x / 2x-1 2) x+6 / x-6 - x^2 / x+6 3) x+9 / x-4 + x+2 / x^2-11x+28 4) x / x^2-64 + 11 / 2x^2+11x-40 5) 5 / x + 11 / x-3 - x-4 / x^2+2x-15

Arectangular lawn is 14m long and 10m wide. a strip of uniform width is mowed around the outside of the lawn. how wide is the strip when the area of the unmowed portion of the lawn is 12m². (the answer is 4m, but i need to know how to solve it)