Evaluate the expression when y = 3 and z = -1/5. 1/2z - 2/3y = ?

Thanks, if you help!
(7th grade ‘algebra’)

The number of hours per week that the television is turned on is determined for each family in a sample. the mean of the data is 37 hours and the median is 33.2 hours. twenty-four of the families in the sample turned on the television for 22 hours or less for the week. the 13th percentile of the data is 22 hours. approximately how many families are in the sample? round your answer to the nearest integer.

Is it true or false i’m trying to pass this test so i can leave school

How is working backward similar to solving an equation?