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You have the system of 2 equations
    a   + b =   14      (1)
    70a + 55b = 905     (2)
From equation (1), express  b = 14-a  and substitute it into equation (2), replacing b there
    70a + 55(14-a) = 905.
From this equation
    a =  = 9.
ANSWER.  9 printing press of the type A and the rest, (14-9) = 5 printing press of the type B.
CHECK.  70*9 + 55*5 = 905 books.   ! Correct !
 = 9.
ANSWER.  9 printing press of the type A and the rest, (14-9) = 5 printing press of the type B.
CHECK.  70*9 + 55*5 = 905 books.   ! Correct !
Solved.