On a spacecraft, two engines fire for a time of 598 s. One gives the craft an acceleration in the x direction of ax = 4.92 m/s^2, while the other produces an acceleration in the y direction of ay = 7.60 m/s2. At the end of the firing period, the craft has velocity components of vx = 3734 m/s and vy = 4804 m/s. Calculate the magnitude of the initial velocity.