How much was a Reverse of guitar of agust n p o barrios before 1998?
CREATE TABLE table_39613 (
    "Value" text,
    "Color" text,
    "Obverse" text,
    "Reverse" text,
    "First issued" real
)
SELECT "Value" FROM table_39613 WHERE "First issued" < '1998' AND "Reverse" = 'guitar of agustín pío barrios'
Below are sql tables schemas paired with instruction that describes a task. Using valid SQLite, write a response that appropriately completes the request for the provided tables. ### Instruction: How much was a Reverse of guitar of agust n p o barrios before 1998? ### Input: CREATE TABLE table_39613 (
    "Value" text,
    "Color" text,
    "Obverse" text,
    "Reverse" text,
    "First issued" real
) ### Response: SELECT "Value" FROM table_39613 WHERE "First issued" < '1998' AND "Reverse" = 'guitar of agustín pío barrios'