First of all we find the value of 10%, so we do 24 ÷ 10 which equals to 2.4, then we find the halved value of 2.4, so we do 2.4 ÷ 2 which equals to 1.2. Then we add 2.4 and 1.2 together, which then gives us 3.6 as the number. We then subtract 3.6 from 24 which gives us 20.4, but we need in money terms so we change it to $20.40. Hope this helps.
