If the total cost of the 4 necklaces was 18.40 then that means in order to find out how much she spent on pendents she needs to subtract the amount of beads from from the total cost so,
18.40-11.20=7.20
And cause she made 4 necklaces she is going to need to divide 7.20 by 4 to find out the cost of money that she had spent on each necklaces pendants.
7.20÷4=1.80
Meaning that she had spent $1.80 on each necklaces pendants
