The only foreign key in this table is customer$\_$id$.$

Which of these statements has a problem that will result in an error?

LAUNCH DATABASE

ALTER TABLE invoice

ALTER COLUMN customer$\_$id

TYPE VARCHAR $(50)$;

ALTER TABLE invoice

ALTER COLUMN total

TYPE VARCHAR $(100)$;

ALTER TABLE invoice

ALTER COLUMN billing$\_$state

TYPE VARCHAR $(100)$;

ALTER TABLE invoice

ALTER COLUMN billing$\_$city

TYPE VARCHAR $(100)$;