On a spacecraft two engines fire for a time of 589 s. One gives the craft an acceleration in the x direction of ax = 5.05 m/s2, while the other produces an acceleration in the y direction of ay = 7.29 m/s2. At the end of the firing period, the craft has velocity components of vx = 3726 m/s and vy = 4857 m/s. Calculate the magnitude of the initial velocity.