7. If each sister has one brother, it would be one brother total, because they are all related. They don't each have their own brother. So mom+dad+sisters(4)+brother=7 total.
If two variables are directly proportional, it means that an increase in the value of one variable would cause a corresponding increase in the other variable. Also, a decrease in the value of one variable would cause a corresponding decrease in the other variable.
Given that x varies directly with y, if we introduce a constant of proportionality, k, the expression becomes
