On a spacecraft two engines fire for a time of 600 s. One gives the craft an acceleration in the x direction of ax = 5.10 m/s2, while the other produces an acceleration in the y direction of ay = 7.30 m/s2. At the end of the firing period, the craft has velocity components of vx = 3565 m/s and vy = 4556 m/s. Find the magnitude and direction of the initial velocity. Express the direction as an angle with respect to the +x axis.