Two streams merge to form a river. One stream has a width of 8.8 m, depth of 3.7 m, and current speed of 2.1 m/s. The other stream is 6.7 m wide and 3.8 m deep, and flows at 2.5 m/s. If the river has width 10.3 m and speed 2.9 m/s, what is its depth