Determine the domain on which the following function is decreasing​

we can set up an equation to find the girls' ages. the equation is         28=0.5x-5+x. (comment if you need me to explain how i got this equation.) so, you add x and 0.5x to get 1.5x and add 5 to each side. your new equation is 33=1.5x. now divide both sides of the equation by 1.5 to get 22=x. because x is mary's age, to find jasmine's age we subtract mary's age from 28. we find that mary is 22 years old and jasmine is 6 years old.