Gabrielle's age is two times Mikhail's age. The sum of their ages is 54. What is Mikhail's age?

What is the first step of an indirect proof of a number that is divisible by two

[10 points, algebra 2-simplifying complex fractions]according to my answer key the restrictions are -1 and 4. but why not positive 1?

Jason went to an arcade to play video games. he paid $2 for every 11 tokens he bought. he spent a total of $16 on tokens. which equation can be used to determine,t, the number lf tokens jason bought