Because it has more mass so with less mass it accelerates faster. That is newtons 2nd law of motion.
80 is 40% of 200 because 40%of 100 is 40. Common sense is just to double both values, also 200 x .40 (40%as a decimal) gives you the result of 80.
255-45-10=200
1 week
200/10=20
20 weeks plus one week equals 21 weeks
Thank you have a day!

Since we need to solve for r we have to leave that variable alone in one side of the equation. We notice that at is adding in the right side, then it goes to the left side substracting, that is:

Therefore:

in the last part we only switch the sides of the equation.