Two tuning forks, with natural frequency $$700\,\text{Hz}$$ each, move relative to a stationary observer. Fork $$1$$ moves towards the observer while fork $$2$$ moves away from the observer. Both the forks move with same velocity $$v$$ on the same line. The observer, standing between the two forks, hears $$4$$ beats per second. Using the speed of sound in air as $$v_s = 350\,\text{m s}^{-1}$$, the speed of each tuning fork is