sql phone screen question

cargurus-interview.sql

create table keywords
(
  id INT PRIMARY KEY NOT NULL AUTO_INCREMENT,
  campaign_id INT
);

create table campaign
(
  id INT PRIMARY KEY NOT NULL AUTO_INCREMENT,
  name varchar
);

create table ledger
(
  entry_date timestamp NOT NULL,
  keyword_id INT,
  clicks INT,
  cost float,
  leads INT
)

/* write query to return the id, name, and amount spent for the 5 top spending campaigns in August 2016 */



/* given ledger table
 entry_date | keyword_id | clicks | cost  | leads | cpc/bid | cpl
 yesterday  | 1          | 10     |  2.50 | 2     | .25     | 1.25
 yesterday  | 2          | 1000   | 350.0 | 35    | .35     | 10.0
 yesterday  | 3          | 300    |  75.0 | 10    | .25     | 7.50

 what should you bid today if your objective is cost/leads = 10.0? */