A man completed a trip of 136 km in 8 hrs. Some part of the trip was covered at 15 km/hr. What is the part of the trip covered at 18 km/hr?

Let the part of the trip covered at 18 km/hr  be x km
Hence the part of the trip covered at 15 km/hr = (136-x)km

Now time taken for covering x km at 18 km/hr = $\frac{x}{18}hrs$
And time taken for covering (136-x)km at 15 km/hr =$\frac{136-x}{15}hrs$

Now it is given that total distance is covered in 8 hrs

$$\begin{gathered} \therefore \frac{x}{18}+\frac{136-x}{15}=8 \\ \Rightarrow \frac{15x+2448-18x}{270} =8 \\ \Rightarrow -3x+2448 =2160 \\ \Rightarrow 3x = 288 \\ \Rightarrow x=96 km \\ Hence part of trip covered at 18 km/hr = 96 km \end{gathered}$$