No problem!
Okay you must set and equation.
$40 × ? = 10
I used multiplication because when things are discounted, they are multiplied by decimals
? = [tex] \frac{10}{40} [/tex]
[tex] \frac{10}{40} [/tex] is equal to [tex] \frac{1}{4} [/tex]
1/4 is 25%
The item needs to be marked down 25% to buy and get a discount of $10