Answer :
so she bought 10 pounds and she need 13 total so
10+x=13
subtract 10 from both sides
x=3
she needs to buy 3 more pounds of potting soil (number of bags depends on how many pounds per bag)
10+x=13
subtract 10 from both sides
x=3
she needs to buy 3 more pounds of potting soil (number of bags depends on how many pounds per bag)