Answer : Option C

Explanation :

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Solution 1
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Given that time taken for riding both ways will be 2 hours lesser than
the time needed for waking one way and riding back
From this, we can understand that
time needed for riding one way = time needed for waking one way - 2 hours
Given that time taken in walking one way and riding back = 5 hours 45 min
Hence The time he would take to walk both ways = 5 hours 45 min + 2 hours = 7 hours 45 min
In fact, you can do all these calculations mentally and save a lot of time
which will be a real benefit for you.
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Solution 2
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$MF#%\begin{align}
&\text{Let the distance be x km. Then}\\\\\\\\
&\text{(Time taken to walk x km) + (Time taken to ride x km) = 5 hour 45 min }\\
&= 5\dfrac{45}{60}\text{ hour = }5\dfrac{3}{4}\text{ hour = }\dfrac{23}{4}\text{ hour .......(Equation1)}\\\\\\\\\\\\\\\\
&\text{(Time taken to ride 2x km) = 5 hour 45 min - 2 = 3 hour 45 min}\\
&= 3\dfrac{45}{60}\text{ hour = }3\dfrac{3}{4}\text{ hour = }\dfrac{15}{4}\text{ hour .......(Equation2)}\\\\\\\\\\\\\\\\
&\text{Solving equations 1 and 2}\\
&\text{(Equation 1 )}\times 2 \Rightarrow \text{(Time taken to walk 2x km)+ (Time taken to ride 2x km) = }\\
&\dfrac{23}{2}\text{ hour .......(Equation3)}\\\\\\\\\\\\\\\\
&\text{(Equation 3 - Equation 2)}\Rightarrow\text{ Time taken to walk 2x km} = \dfrac{23}{2} - \dfrac{15}{4} \\
&= \dfrac{46}{4} - \dfrac{15}{4} = \dfrac{31}{4}\text{ hours = }7\dfrac{3}{4}\text{ hours = }7\text{ hours 45 minutes }\\
\end{align} $MF#%