Question 548293
It looks like you have already done the hard part of the question..(the equation)

If we let time 0 be 7AM.  We know at this time we have 6 inches of snow (this is like the y-intercept)  the rate of 0.5 is the slope as for every hour we go up 0.5 inches.   

The graph looks like this:
{{{graph(300,300,-10,10,0,10,6+0.5x)}}}

Now at 11PM the night before, how many hours passed to get to time 0 (7AM)?  
If you think about it long enough 7+1=8 hours passed (so our x value is -8)  

All we need to see is what the y value is when x=-8
This could be seen on the graph, but if you are like me and your graphs aren't perfect like the computer shows them... theres another way 

{{{y=6+0.5*x}}}
{{{y=6+0.5*(-8)}}}
{{{y=2}}}


So 2 inches will be there at 11PM the night before.  

MENTAL CHECK:   If you ended up with a negative number, thats not good.. theres no such thing as a negative amount of snow... our answer passes the mental check!