3 tables sum divided by a minus between two fields SQL

hello, i got this three tables on the united on the query and i'm trying to group the value by matricula, but it's saying matricula is ambiguous here's my code.

JOIN (
            SELECT matricula, (total)/(kmsTotais) AS custoKM
            FROM (
                SELECT matricula, SUM(kmfim - quilometragem) AS kmsTotais
            FROM formulario
            GROUP BY matricula
        ) e
        JOIN (
            SELECT matricula, abastecimento_euros as total FROM formulario
        UNION ALL
            SELECT matricula, custo as total FROM viaverde
        UNION ALL
            SELECT matricula, valor as total FROM reparacoes
        ) as subquery
        GROUP BY matricula
        ) i ON i.matricula = f.matricula