Question

if Marianne bought 10 pounds of of potting soil and her father tells her he needs 13 pounds of potting soil how much additional bags should he buy

Answer 1

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)