Let M be the number of homework assignment in math class, and 

    let S be the number of assignments in Science. 


    Then   M = .


    It is the literal translation of English to Math.

    This sentence is INCORRECT from the point of view of English grammar.


    The correct sentence is THIS (my editing) :


        There was twice as much English homework  as the sum of all the Science 
        and Math homework. How many homework assignments are there in English class?


    The answer is

        E = 2*(S + M),

    using obvious designations.