A person covers the first 90 km at a speed of 40 km/h, the next 180 km at a speed of 60 km/h and the next 120 km at a speed of x km/h. . If his average speed for the entire journey is 57\(\frac{7}{9}\) km/h, then what will be the value of x?
1
80
2
75
3
72
4
90