Question about semi-major axis mean separation
The semi major axis $a$ of an orbit is the same as the arithmetic average of the minimum and maximum distance $r$ or the object from the central object in sense of $a = 0.5\cdot(r_{min} + r_{max})$; thus semi major axis is sometimes also called mean separation. As such you are given the sum of the semi major axis of two components.
A two-body problem can be reduced / simplified to a mass-less body circling an object of the combined mass - as such you can calculate the combined mass of both stars with the numbers you are given.