First, I want to thank you for attempting the problem yourself before asking us for help. Lets compare the answer you got with the book's answer.
When solving for t, you want to isolate the t terms. First, subtract 2s on both sides of the equation.
r - 2s = -2t
Then divide both sides of the equation by -2 to get a coefficient of 1 for t.
(-r + 2s) / 2 = t
when rearranging the terms, you get
(2s - r) / 2 = t
This is the answer you got, which is correct. The book divided each term of the numerator part by 2 (similar to subtracting fractions with common denominator), resulting in
(2s / 2) - (r / 2) = t
s - (r / 2) = t ----> book's answer
The book just put your in a different form. You are correct.
Question 2 is same situation.