Answer :
Step 1:
Given data
On a winding road
Average speed = x
Time = 3hours
[tex]\begin{gathered} \text{Distance travelled = Average sp}eed\text{ }\times\text{ Time} \\ =\text{ 3x miles} \end{gathered}[/tex]On Level road
Average speed = 20 + x
Time = 3 hours
[tex]\begin{gathered} \text{Distance travelled = Average sp}eed\text{ }\times\text{ Time} \\ =\text{ 3(20 + x)} \\ =\text{ 60 + 3x miles} \end{gathered}[/tex]Step 2:
Total distance traveled = 330 miles
[tex]\begin{gathered} 3x\text{ + 60 + 3x = 330} \\ 6x\text{ + 60 = 330} \\ 6x\text{ = 330 - 60} \\ 6x\text{ = 270} \\ x\text{ = }\frac{270}{6} \\ x\text{ = 45 miles/hour} \end{gathered}[/tex]Final answer
Average speed of the level road = x + 20 = 45 + 20 = 65 miles per hour
Average speed of the level road = 65 miles