Question 807625
{{{x}}}= time spent doing English homework (in minutes).
{{{y}}}= time spent doing Math homework (in minutes).
Of course, {{{x>=0}}} and {{{y>=0}}} .
It is not reasonable to have negative numbers for {{{x}}} or {{{y}}} .
Negative values do no make sense for either variable.
{{{x+y=9}}} --> {{{highlight(y=90-x)}}}
The domain and range of that function are
{{{0<=x<=90}}} and {{{0<=y<=90}}}