Which of these are accepted as a true without proof?

Two variables, x and y, vary inversely, and x=12 when y=4. what is the value of y when x=3?

Mr. brettler is hanging up a 5-foot tall rectangular welcome sign in the gym. he has drawn a sketch on a coordinate grid. he has the lower vertices of the sign at (9, –3) and (–6, –3). where would the upper vertices be on the grid?

Cody was 165cm tall on the first day of school this year, which was 10% taller than he was on the first day of school last year.