Question 1173443
let x = the number of 3 dollars boxes.
let y = the number of 5 dollar boxes.


your equation will be 3x + 5y <= 20


the number of 5 dollars boxes is 1 less than the number of 3 dollars boxes.


the equation for that is y = x - 4


in the equation of 3x - 5y <= 20, replace y with x - 4 to get 3x + 5(x-4) <= 20


simplify this equation to get 3x + 5x - 20 <= 20


add 20 to both sides of this inequality and combine like terms to get 8x <= 40


solve for x to get x <= 5


since y = x - 4, then y <= 1


when x = 5, y = 1


3x + 5y <= 20 becomes 3*5 + 5*1 <= 20 which becomes 20 <= 20 which is true.


any value of x < 5 will result in y being equal to 0.


if she wants at least one 5 dollar box, then x must be equal to 5.