You get 493.41 when
you subtract 15.54 from 508.953 using the rules for significant figures.
For addition
and subtraction, look at the decimal portion (i.e., to the right of the decimal
point) of the numbers ONLY. Here is what to do:
1) Count the
number of significant figures in the decimal portion of each number in the
problem. (The digits to the left of the decimal place are not used to determine
the number of decimal places in the final answer.)
2) Add or
subtract in the normal fashion.
3) Round the
answer to the LEAST number of places in the decimal portion of any number in
the problem.
The correct answer between all the choices given is the
third choice or letter C. I am hoping that this answer has satisfied your query
and it will be able to help you in your endeavor, and if you would like, feel
free to ask another question.
When you work out it helps clear your thoughts and think of nothing. It makes you feel good.
Running because kinetic energey is the engery created by motion
The non-relativistic formula for kinetic energy for low speeds is :
K.E = 0.5mv^2 = 0.5 * 22 * (5)^2 = 275 J
The distance covered by car is equal to (assuming it is moving by uniform motion) the product between the car's speed and the time of the car ride, 4 h:

where

is the car's speed

is the duration of the car ride
Similarly, the distance covered by train is equal to the product between the train's speed and the duration of the train ride, 7 h:

The total distance covered is S=255 km, which is the sum of the distances covered by car and train:

which becomes

(1)
we also know that the train speed is 5 km/h greater than the car's speed:

(2)
If we put (2) into (1), we find

and if we solve it, we find


So, the car speed is 20 km/h and the train speed is 25 km/h.