Write the compound inequality: " A number n is less than or equal to -7 or greater than 12

Let the number be n, then -1<3n+5<38 or -1≤3n+5≤38 depending on what is meant by “between”. We’ll assume the former.

-1<3n+5<38, subtract 5 throughout: -6<3n<33, divide through by 3: -2<n<11, shows the number to be in the range (-2,11) or possibly [-2,11].

it's undefined because anything multiplied by 0 is 0. that said, 7 days is 168 hours