What was the difference between the speed of vehicles A on Day 1 and the speed of vehicles C on the same day ?

Answer: Option C

$$\begin{array}{rl}& \text{Speeds of vehicles on Day 1:}\\ & \text{A → }\frac{832}{16}\text{ km/hr}=\text{52 km/hr}\\ & \text{B → }\frac{516}{12}\text{ km/hr}=\text{43 km/hr}\\ & \text{C → }\frac{693}{11}\text{ km/hr}=\text{63 km/hr}\\ & \text{D → }\frac{552}{12}\text{ km/hr}=\text{46 km/hr}\\ & \text{E → }\frac{935}{17}\text{ km/hr}=\text{55 km/hr}\\ & \text{F → }\frac{703}{19}\text{ km/hr}=\text{37 km/hr}\\ & \\ & \text{Speed of vehicles on Day 2:}\\ & \text{A → }\frac{864}{16}\text{ km/hr}=\text{54 km/hr}\\ & \text{B → }\frac{774}{18}\text{ km/hr}=\text{43 km/hr}\\ & \text{C → }\frac{810}{18}\text{ km/hr}=\text{45 km/hr}\\ & \text{D → }\frac{765}{15}\text{ km/hr}=\text{51 km/hr}\\ & \text{E → }\frac{546}{14}\text{ km/hr}=\text{39 km/hr}\\ & \text{F → }\frac{636}{12}\text{ km/hr}=\text{53 km/hr}\end{array}$$

Difference between the speed of A on Day 1 and speed of C on Day 1
= (63 - 52) km/hr
= 11 km/hr