Bert was selling books at school. the first week he sold 3 more than two times the numbers of books he sold the second week. during the two week period he sold 18 books. how many books did he sale the first week of the fundraiser?

3 moer than (3+) 2 times the numbe of books he sold in the second week (2 times second week)
first week=3+(2 time 2nd week)

total ie sold 18

so
first week+second week=18
3+(2 times 2nd week)+2nd week=18
solve
minus 3 both sides
3-3+(2 times 2nd week)+2nd week=18-3
0+(2 times 2nd week)+2nd week=15
(2 times 2nd week)+2nd week=15

add
3 times 2nd week=15
divide both sides by 3
2nd week=5

sub back
first week+second week=18
first week+5=18
minus 5
first week=13

he sold 13 in the first week