In this case the answer is very simple. .
Step 01:
Data
total distance = 422 mi
total time = 6 hours
Step 02:
[tex]\frac{total\text{ distance}}{\text{total time}}=\frac{422mi}{6\text{ hour}}\text{ = }70.33\text{ mi / hour}[/tex]The answer is:
Joshua's speed was 70 mi/hours