Find the x- and y- intercepts of the graph -2x+9y+36

You don't have a graph there, or an equation from which
a graph could be drawn.  You just have an expression that
stands for a number.  If you go on to say that the expression
is equal to something, then there are only certain values of
'x' and 'y' that can make it true, and those values make the graph.

Once you have the equation, you get the x- and y-intercepts
like this:

-- Set  y=0  in the equation, and solve it for 'x'.
    That's the x-intercept. 

-- Set  x=0  in the equation, and solve it for 'y'.
    That's the y-intercept.